and show that In the isosceles triangle PQR, PQ = 2 and the angle QPR = angle PQR 1 radians. The area of triangle PQR is denoted by A.

Transcription

1 H Mathematics 07 Prelim Eam Paper Question Answer all questions [00 marks]. n n Given that k!( k ) ( n )! n, find ( k )!( k k ). [] k k A geometric sequence U, U, U,... is such that T, T, T,... U and has a common ratio of e. Another sequence U lnt for all r. r r (i) Prove that the sequence U, U, U,... is arithmetic. [] A third sequence W, W, W,... is such that W W U for all r. r r r W and (ii) By considering n ( Wr Wr), show that r Wn ( n n ). [] Using an algebraic method, find the set of values of that satisfies the inequality Hence solve. [] []. 4 R P Q In the isosceles triangle PQR, PQ = and the angle QPR = angle PQR π radians. The area of triangle PQR is denoted by A. Given that is a sufficiently small angle, show that A tan, tan a b c for constants a, b and c to be determined in eact form. [5]

2 Blank Page 5 (a) Given that cosec y d for (cosec ) d ( ) 0 y π, for find dy d in terms of y. Deduce that. [] (b) The function f is such that f ( ) and f '( ) eist for all real. Sketch a possible graph of f which illustrates that the following statement is not necessarily true: If the equation f ( ) as f '( ) 0 has eactly one root 0 and f ''(0) 0, then. [] 6 (a) State a sequence of transformations that transform the graph of ( y ) to the graph of ( ) y. [] (b) The diagram below shows the curve and intersects the -ais at ( 4, 0), y 0 and y. y y f ( ). It has a maimum point at (4, ) and the origin. The curve has asymptotes y = + (4, ) 4 O = Sketch on separate diagrams, the graphs of (i) y f '( ), [] (ii) y, f ( ) [] including the coordinates of the points where the graphs cross the aes, the turning points and the equations of any asymptotes, where appropriate. 7 (i) Epress sin cos as Rsin ( ), where R 0 and is an acute angle. [] Blank Page

3 The function f is defined by f : sin cos,, π π. 6 (ii) Sketch the graph of y f ( ). [] (iii) Find f ( ) sketch the graph of, stating the domain of y f. On the same diagram as in part (ii), f ( ), indicating the equation of the line of symmetry. (iv) Using integration, find the area of the region bounded by the graph of and the aes. [] The function g is defined by g : ln( ), for,. f [4] (v) Show that the composite function gf eists, and find the range of gf. [] 8 Do not use a graphic calculator in answering this question. (a) y O It is given that f ( ) is a cubic polynomial with real coefficients. The diagram shows the curve with equation y f ( ). What can be said about all the roots of the equation f( ) 0? [] (b) The equation z (7 6i) z ic 0, where c is a non-zero real number, has a root z 4i. Show that c. Determine the other root of the equation in cartesian form. Hence find the roots of the equation w 6 7i w i 0. [6] i (c) The comple number z is given by z e. i e. [] (i) Show that z can be epressed as cos

4 Blank Page 9 The line (ii) Given l z w *. π and w i, find the eact modulus and argument of passes through the point A, whose position vector is 7 parallel to the vector 4 y z5. The plane p contains is perpendicular to p. i jk l. The line and is parallel to (i) Find the cartesian equation of (ii) Find the distance of (iii) Find the equation of l p to p. l i j k [5], and is is given by the cartesian equation l. Another plane p also contains l and p. [] [] in the scalar product form. [] A particle P moves along a straight line c which lies in the plane through a point (5,, ). another straight line d in between c and l. P hits the plane p p. The angle between d and p and c passes at A and rebounds to move along l is the same as the angle (iv) Find the direction cosines of d. [6] (v) Another particle, Q, is placed at the point (,, ). Find the shortest 5 distance PQ as P moves along d. [] 0 y Cannonball (, y) O Ground The diagram shows the trajectory of a cannonball fired off from an origin O with an initial speed of v ms and at an angle of above the ground. At time t seconds, the position of the cannonball can be modelled by the parametric equations ( vcos ) t, y ( vsin ) t 5 t, where m is the horizontal distance of the cannonball with respect to O and y m is the vertical distance of the cannonball with respect to ground level. (i) Find the horizontal distance, d m, that a cannonball would have travelled by the time it hits the ground. Leave your answer in terms of v and. [4] Use v 00 to answer the remaining parts of the question. An approaching target is travelling at a constant speed of 0 ms - along the ground. A cannonball is fired towards the target when it is 000 m away. You may assume the height of the moving target is negligible. Blank Page

5 (ii) Show that in order to hit the target, the possible angles at which the cannonball should be fired are.7 and [] (iii) Eplain at which angle the cannonball should be fired in order to hit the target earlier. [] (iv) Given that the horizontal when.7, find the angle that the tangent to the trajectory makes with 70. [4] For this question, you may leave your answers to the nearest dollar. (a) Mr Foo invested $5,000 in three different stocks A, B and C. After a year, the value of the stocks A and B grew by % and 6% respectively, while the value of stock C fell by %. Mr Foo did not gain or lose any money. Let a, b and c denote the amount of money he invested in stocks A, B and C respectively. (i) Find epressions for a and b, in terms of c. [] (ii) Find the values between which c must lie. [] (b) Mr Lee is interested in growing his savings amount of $55,000 and is considering the Singapore Savings Bonds. He is able to enjoy a higher average return per year when he invests over a longer period of time as shown in the following table. Number of years invested Average return per year, % For eample, if Mr Lee invests for two years, he is able to enjoy compound interest at a rate of.% per year. (i) Calculate the compound interest earned by Mr Lee if he were to invest $55,000 in this bond for a period of five years. [] A bank offers a dual-savings account with the following scheme: For every $,000 deposited into the normal savings account, an individual can deposit $0,000 into the special savings account to enjoy a higher interest rate. The annual compound interest rates for the normal savings account and the special savings account are 0.9% and.8% respectively. Mr Lee is interested in setting up this dual-savings account and considers an n- year investment plan as such: At the start of each year, he will place $,000 in the normal savings account and $0,000 in the special savings account. (ii) Find the respective amount of money in the normal savings account and special savings account at the end of n years. Leave your answers in terms of n. [4] 5

6 Blank Page (iii) Find the least value of n such that the compound interest earned in dualsavings account is more than the compound interest earned in part (i). [] End Of Paper Blank Page

7 ANNEX B DHS H Math JC Preliminary Eamination Paper QN Topic Set Answers Sigma Notation and Method of Difference ( n + )! n Sigma Notation and Method of Difference -- Equations and Inequalities { or 4} < ; 4 Maclaurin series ( ) 5 Differentiation & Applications or < or < or + 4θ + 4 θ (a) (b) dy = d cosec y cot y y 6 Graphs and Transformation (a). Translate units in the positive -direction. Translate units in the negative y-direction. Scale by a factor of parallel to the y-direction Alternative. Scale by a factor of parallel to the y-direction. Translate units in the negative y-direction

8 (b)(i) y y = (b) (ii) 7 Functions (i) sin + cos = sin( + π) (ii) y y = y = f() O y = f - () (iii) f ( ) = π + sin ( ); D = R = [0,] (iv) (v) R = [0, 0.96] gf f f

9 8 Comple numbers (a) Since the curve shows only one -intercept, it means that there is only one real root in the equation f ( ) = 0. Since the equation has all real coefficients, then the two other roots must be non-real and they are a conjugate pair. (b) i ; 4 i and i. (c) (ii) π ; Vectors (i) y z = 7 (ii) 7 (iii) r. 8 = (iv) 6 8, and or , and Differentiation & Applications (v) 5 40 =. ( s.f.) 9 55 (i) v sinθ cosθ 5 (ii) (iii).7 (iv) 7. (to dp) AP and GP (a)(i) a = 7500 c, b = c 500 (ii) between 500 and 8750 (b)(i) 454 (to the nearest dollar) (ii) Normal savings account:575.79(.009 n ) (iii) 7 Special savings account: (.08 n )

10 H Mathematics 07 Prelim Eam Paper Solution Method Consider replace k by ( k ) : n k n k k k k k k!( )!( ) k k Method n n k!( k ) n = k!( k )!( ) k k ( n)! n n k! k k! k k k0 n k! k k k 0 n! n n n k! k k k! k k k k0 (i) To prove AP, consider U U r (lnt ) (ln T ) r r ln Tr ln e = T r r n! n 0! 0 0 Since difference is a constant, the sequence is arithmetic. (Proven) n n ( W W ) U r r r r r

11 n LHS ( W W ) W W W W W r 4 n n W n W W W : W W RHS = n n r U r U U... U n r n (() ( n )) nn ( ) nn ( ) Thus, Wn Wn n n (shown) (i) r Set of values of : or 4

12 (ii) Let y. y y y y or y 4 Method : Usin g y graph y 4 - O The range of values of is or or or Method : Using definition of Since For or For 4 or Hence, the range of values of is or or or 4 R h P Q

13 4 5 π h tan π π A tan tan π tan tan tan (shown) π tan tan tan 4 4 cos ec y Diff wrt : dy cos ec y cot y d dy d cos ec y cot y dy Using cot y cosec y, d cos ec (cos ec ) y y π [since 0 y tan y 0 cot y 0 (shown) cot y (cos ec y) ] Since y cos ec, dy d (cosec ) d d

14 5 Alternative cosec y Diff wrt : dy cos ec y cot y d dy d cosec y cot y Since cos ec y, sin y y sin y By constructing the right angle triangle, tan y dy tan y d cos ec y cot y cosec y (shown) (b) y k O 6 (a) y Replace by y y Replace y by y Replace y by y y

15 6. Translate units in the positive -direction. Translate units in the negative y-direction. Scale by a factor of parallel to the y-direction Alternative:. Scale by a factor of. Translate (b) (i) parallel to the y-direction units in the negative y-direction y y = O (4, 0) y = 0 = (b) (ii) y y = 0 (,0) O (4, /) = 4 = 0

16 7 7 (i) Using R formula, sin cos sin( π) (ii) y y = y = f() O y = f - () (iii) To find f - : Let ysin( π) π sin ( y) f ( ) sin ( ) D R [0, ] f f (iv) For the area bounded by the graph of y = f() y f and the aes: O y = f - () By symmetry, Area 0 0 f ( ) d (sin cos ) d π π 0 cos sin 0 π

17 8 (v) gf eists if Since R [ π, π] - f g 6 D (, ), Ie. R D f - g gf R D f - g eists. To find the range of gf : Method (two stage mapping method) D R R f g - - f f gf [0,] [ π, π]? 6 R [0, 0.96] gf Method (find gf ) (need to use GC to see shape)

18 9 gf ( ) ln( π sin ( )) D D [0, ] gf f gf R [0,0.96] 8 (a) Since the curve shows only one -intercept, it means that there is only one real root in the equation f( ) 0. Since the equation has all real coefficients, then the two other roots must be nonreal and they are conjugate pair. (b) Since z 4i is a root of z (7 6i) z ic 0, ( 4i) (7 6i)( 4i) ic 0 (9 4i 6) ( 8i 8i 4) ic 0 Comparing the Im - part, c 0 c (shown) Since z 4i is a root of z (7 6i) z i 0, (7 6i) i ( 4i), where z z z z a a Comparing the coefficient of constant term, i a( 4i) i 4i i 5 50i a i 4i 5 5 z ( i) 0 z i Therefore, the other root is i.

19 0 Replace z by (i w) 7 6i (i w) i 0 iw w 6 7i w i 0 w 6 7i w i 0 iw 4i w 4 i or iw i w i The roots of the equation are 4 i a bi. and i Alternative Method: z (7 6i) z i 0 Let the other root be 7 6i 7 Sum of the roots = 4ia bi i Comparing real and imaginary parts: 7 a a 4 b b The other root is i (c) (i) z e i i i i + i i e (e e ) e Ree i cos e (shown) Alternative Method: z e i i i i e (e + e ) e i i cos isin cos isin e cos isin cos isin i cos e (shown).

20 Alternative Method: i z e cos isin cos cos isin cos i sin cos i cos e (shown) (ii) * z w cos z z 6 w w 8 9 * z z arg arg arg( z) arg( w) w w 6 z arg w * 6 (i) A vector equation of l is r 7 4, y z5 Let =., y, z 5 Then a vector equation of l is r, 5 A vector perpendicular to p is / / 0

21 Eqn of p : r Cartesian eqn : y z 7 (ii) Distance of a line // to a plane is the distance between a point on this line to the plane Required distance F A(,7,) Distance of l to p BF AB. 4. Alternative : Equation of line BF: r 5 OF for some 5 As F lies in, Distance of l to p 9 BF OF OB 9 9

22 (iii) A vector perpendicular to p Equation of p 7 7 r (iv) A Q c N e G d line d is a reflection of line c in the line e which passes through A, is perpendicular to l and p and lying in p. Eqn of line e : r 7 Foot of perpendicular, N, from 5,, to line e

23 ON ON OG OG ' 8 5 OG ' AG ' / / Direction cosines of line d are, and or, and [Alternative to find ON - intersection of lines] Eqn of line e : r 7 5 Eqn of line GN: r At N,

24 Solving,.5, 8 5 ON (v) Shortest distance from Q to line d 6 AQ ( s.f.) (i) To determine range of cannonball, we consider y = 0: 0 ( vsin ) t 5t 0 t vsin 5t t 0 (rejected) or vsin 5t 0 vsin t 5

25 6 When vsin t 5 ( v cos ) t, vsin ( v cos ) 5 v sin cos v sin cos d 5 5 (ii) Trajectory of cannonball Target (0m/s) O 000 m Ground Time taken for cannonball to hit the ground = time taken for the target to reach the point of impact of the cannonball. vsin 000 d 5 0 v sincos vsin (00) sincos 400sin Possible angles are.7 (to dp) or 69.5(to dp). (shown) vsin vsin.7 vsin 69.5 (iii) Since t when cannon hits target and Therefore to hit target earlier, cannonball should be fired at.7. (iv) (00cos.7 ) t y (00sin.7 ) t 5t d dy t dt dt dy 77.80t d 84.5 When 70, 84.5t 70 t.005 dy (.005) d 84.5 Let the required angle be. tan (to dp)

26 7 (a)(i) a b c () 0.0a 0.06b 0.0c () [or.0a.06b 0.98c 5000] Solving SLE, a 7500 c bc500 (ii) Since a and b must both be positive, it implies that c must lie between 500 and (b)(i) Since Mr Lee invested in a period of five years, the average return per year will be.6%. Total amount of interest earned 5 (.06) (55000) (to the nearest dollar) (ii) Amount of money in the normal savings account at the end of n years n 000( ) n (.009).009 n = (.009 ) Amount of money in the special savings account at the end of n years n (.08).08 = n (iii) Total interest earned from dual-savings account n n = (.009 ) n n n (.009 ) n 454 From GC, 7 n Least value of n is 7.

27 (i) Find d tan. d Hence evaluate 4 π sec tan tan e d, leaving your 0 answer in eact form. [] (ii) By epressing ) 7 d. as m (9 4 ) where m is a constant, find [] The curve C with equation y oblique asymptote y. a a, where a is a constant, has the (i) Show that a =. Hence sketch C, giving the equations of any asymptotes and the eact coordinates of any points of intersection with the aes. [] (ii) The region bounded by C for and is rotated through π radians about the line By considering a translation of C, or otherwise, find the volume of revolution formed. [5] and the lines. The variables y and satisfy the differential equation y, y y 4 dy ln d ln. (i) Show that the substitution du u. dy Given that y 0 when, show that ln u reduces the differential equation to ln y ln. [6] ln The curve C has equation y ln. and two asymptotes y a and b. It is given that C has a maimum point (ii) Find the eact coordinates of the maimum point. [] (iii) Eplain why a 0. [You may assume that as, ln 0. ] [] (iv) Determine the value of b, giving your answer correct to 4 decimal places. [] (v) Sketch C. []

28 Blank Page 4 Referred to the origin O, the points A and B have position vectors a and b, where a and b are non-zero and non-parallel. The point C lies on OB produced such that OC 5 OB. It is given that a b and cos AOB. (a) (i) Show that a vector equation of the line AC is 4 r a a 5 b, where is a real parameter. [] The line l lies in the plane containing O, A and B. (ii) Eplain why the direction vector of l can be epressed as where s and t are real numbers. [] sa tb, Given that l is perpendicular to AB, show that t. s [4] Given further that l passes through B, write down a vector equation of l, in a similar form as part (i). [] (iii) Find the position vector of the point of intersection of line AC and l, in terms of a and b. [] (b) Eplain why, for any constant k, ( a k b) b gives the area of the parallelogram with sides OA and OB. Find the area of the parallelogram, leaving your answer in terms of a. [4] 5 A new game has been designed for a particular casino using two fair die. In each round of the game, a player places a bet of $ before proceeding to roll the two die. The player s score is the sum of the results from both die. For the scores in the following table, the player keeps his bet and receives a payout as indicated. Score Payout 9 or 0 $ or 4 $5 $8 For any other scores, the player loses his bet. Let X be the random variable denoting the winnings of the casino from each round of the game. (i) Show that E( X ) and find Var( X ). [4] (ii) X is the mean winnings of the casino from n rounds of this game. Find P( X 0) when n 0 and n Make a comparison of these probabilities and comment in contet of the question. [] Blank Page

29 6 The students in a college are separated into two groups of comparable sizes, Group X and Group Y. The marks for their Mathematics eamination are normally distributed with means and variances as shown in the following table. Mean Variance Group X 55 0 Group Y 4 5 (i) Eplain why it may not be appropriate for the mark of a randomly chosen student from the college population to be modelled by a normal distribution. [] (ii) In order to pass the eamination, students from Group Y must obtain at least d marks. Find, correct to decimal place, the maimum value of d if at least 60% of them pass. [] (iii) Find the probability that the total marks of 4 students from Group Y is less than three times the mark of a student from Group X. State clearly the mean and variance of the distribution you use in your calculation. [] (iv) The marks of 40 students, with 0 each randomly selected from Group X and Group Y, are used to compute a new mean mark, M. Given that P( M 44.5 k) , find the value of k. [4] State a necessary assumption for your calculations to hold in parts (iii) and (iv). [] 7 The company Snatch provides a ride-hailing service comprising tais and private cars in Singapore. Snatch claims that the mean waiting time for a passenger from the booking time to the time of the vehicle s arrival is 7 minutes. To test whether the claim is true, a random sample of 0 passengers waiting times is obtained. The standard deviation of the sample is minutes. A hypothesis test conducted concludes that there is sufficient evidence at the % significance level to reject the claim. (i) State appropriate hypotheses and the distribution of the test statistic used. [] (ii) Find the range of values of the sample mean waiting time, t. [] (iii) A hypothesis test is conducted at the % significance level whether the mean waiting time of passengers is more than 7 minutes. Using the eisting sample, deduce the conclusion of this test if the sample mean waiting time is more than 7 minutes. []

30 Blank Page 8 A retail manager of a large electrical appliances store wants to investigate the relationship between the monthly advertising ependiture, hundred dollars, and the monthly sales of their refrigerators, y thousand dollars. The table below shows the results of the investigation y (i) The manager concludes that an increase in monthly advertising ependiture will result in an increase in the monthly sales of refrigerators. State, with a reason, whether you agree with his conclusion. [] (ii) Draw a scatter diagram to illustrate the above data. Eplain why a linear model is not likely to be appropriate. [] It is thought that the monthly sales y thousand dollars can be modelled by one of the formulae where a and b are constants. y a b e or y a b (iii) Find, correct to 4 decimal places, the value of the product moment correlation coefficient between (A) e and y, (B) and y. Eplain which of y a be or y a b is the better model. [] Assume that the better model in part (iii) holds for part (iv). (iv) The manager forgot to record the monthly advertising ependiture when the monthly sales of refrigerators was $00. Combining this with the above data set, it is found that a = and b = for the model. Find the monthly advertising ependiture that the manager forgot to record, leaving your answer to the nearest hundred. [] 9 A sample of 5 people is chosen from a village of large population. (i) The number of people in the sample who are underweight is denoted by X. State, in contet, the assumption required for X to be well modelled by a binomial distribution. [] (ii) On average, the proportion of people in the village who are underweight is p. It is known that the mode of X is. Use this information to show that p. [] Blank Page

31 000 samples of 5 people are chosen at random from the village and the results are shown in the table below Number of groups (iii) Using the above results, find. Hence estimate the value of p. [] You may now use your estimate in part (iii) as the value of p. (iv) Two random samples of 5 people are chosen. Find the probability that the first sample has at least 4 people who are underweight and has more people who are underweight than the second sample. [] 0 (a) The word DISTRIBUTION has letters. (i) Find the number of different arrangements of the letters that can be made. [] (ii) Find the number of different arrangements which can be made if there are eactly 8 letters between the two Ts. [] One of the Is is removed from the word and the remaining letters are arranged randomly. (iii) Find the probability that no adjacent letters are the same. [4] (b) The insurance company Adiva classifies 0% of their car policy holders as low risk, 60% as average risk and 0% as high risk. Its statistical database has shown that of those classified as low risk, average risk and high risk, %, 5% and 5% are involved in at least one accident respectively. Find the probability that (i) a randomly chosen policy holder is not involved in any accident if the holder is classified as average risk, [] (ii) a randomly chosen policy holder is not involved in any accident, [] (iii) a randomly chosen policy holder is classified as low risk if the holder is involved in at least one accident. [] It is known that the cost of repairing a car when it meets with an accident has the following probability distribution. 5

32 Blank Page Cost incurred (in thousand dollars) Probability It is known that a low risk policy holder will not be involved in more than one accident in a year. You may assume that there will be no cost incurred by the company in insuring a holder whose car is not involved in any accident. (iv) Construct the probability distribution table of the cost incurred by Adiva in insuring a low risk policy holder assuming that the cost of repairing a car is independent of a low risk policy holder meeting an accident. [] (v) In order to have an epected profit of $00 from each policy holder, find the amount that Adiva should charge a low risk policy holder when he renews his annual policy. [] Blank Page

33 H Mathematics 07 Preliminary Eam Paper Solution 4 tan 4 tan (i) sec tan e d sec tan e d 0 0 e e (ii) d d d 9 4 tan 4 tan e 4 e tan 0 sin 9 4 C a a (i) y a ( a) Given that oblique asymptote is y, a (shown) Alternative a a b Let ( ) a a b Comparing coeff of : a 0 a (shown) and b 0 y ( ) HA: OA: y (given)

34 y (0,) (ii) y (,4) y = 4 y = replace with ( ) y y

35 ( ) y y ( y) 0 ( y) ( y) 4()() ( y ) y 4y 8 (reject -ve root) 4 ( y ) y 4y 8 Volume = dy () = 9.75 units ( s.f) ln du ln (i) u d du du d ln ln ln dy d dy ln du u (shown) dy du ln u y c u dy, c is an arbitrary constant u e e e y c c y u Ae y, A is an arbitrary constant ln Ae y y0, : A ln y e ln y ln (shown) Alternative du ln u y c u dy, c is an arbitrary constant With the boundary condition u0, y 0, we see that u 0 Thus ln u y c and c ln dy ln (ii) d ln

36 4 When d y 0, ln 0 e d, y ln e Therefore the maimum point is e, ln. e ln (iii) y ln ln When, 0. ln y ln ln 0. Thus (shown) (iv) For a 0 y b 0.46, ln 0 ln Alternative dy ln When y is undefined, is undefined. d ln Thus ln 0. Since 0 for ln to be defined, ln 0. (v) y O

37 5 4 (a) A a O b B C (i) OC 5 b AC 5 b a 5 b a / /5 b a r a a 5 b, Equation of line AC: (ii) Since l lies on the plane containing O, A and B, its direction vector is coplanar with a and b, thus it will be a linear combination of a and b, i.e. s t a b is a direction vector for l. (iii) Let intersection point be D. At D, a a 5 b b ( a b ) Since a and b are non-zero, non-parallel vectors, () 5 () Solving, , OD a b (b)

38 6 Method Since the base length (OB) and perpendicular height remain the same, the area of parallelograms formed by different k remains the same as the area of the parallelogram with sides OA and OB. Method ( a kb) b ab kbb ab 0 ab Area of parallelogram a b a b sin a a a 5 (i) P(X = ) E( X ) Var( ) E( ) E( ) X X X or 9.08 (to sf) 44 (ii) Since n is large, For n = 0, P X (to sf) For n = 50000, P X 0.00 (to sf) X 07 N, approimately by Central Limit Theorem. 44n The more rounds this game is played, the higher the chance of casino receiving a positive average winnings. In other words, it is almost certain that casino will win in the long run. 6 (i) The distribution may become bimodal when the data for both groups are combined (ii) Let Y be the score of a random student from Group Y. Y ~ N(4, 5) P( Y d) 0.6 P( Y d) 0.4

39 7 d.7 When P( Y d c ) 0.4,. Thus d.7. The maimum mark is.7 (iii) Y X Y X (iv) c 4 E i 4E E 9 4 Var Yi X 4Var Y 9Var X 80 4 Y X ~ N 9,80 i 4 4 P( Y X ) P( Y X 0) (to sf) i 0 0 i i i M i X Yi 40 0E( X) 0E( Y) EM E( X ) E( Y ) Let Var M 0Var( X) 0Var( Y) 600 Var( X ) Var( Y ) M ~ N 44.5, Since P( M 44.5 k) P( M 44.5 k) k k.50 ( s.f) Alternative M ~ N 44.5, Since P( M 44.5 ) k ( sf) Marks of students are independent of one another. 7 (i) Let be the mean of X. H : 7 0 H : 7

40 s sample variance Under H0, since the sample size is large, the test statistic is 4 T N7, approimately by Central Limit Theorem. 9 (ii) Since the claim is rejected i.e. to reject H0 at % significance level c 7 c From GC, c 6.04 t 6.04 or t 7.96 and c (iii) From the two tail test, we know that p-value (two tail) 0.0. For a one-tail test, p-value (two tail) p-value(one tail) , therefore we reject H0 and conclude that there is sufficient evidence at % significance level to say that mean waiting time is more than 7 minutes. Alternatively, From the two tail test and t 7, P( T t) Thus, P( T t) p-value for one-tail test = P( T t) 0.0. Therefore we reject H0 and conclude that there is sufficient evidence at % significance level to say that mean waiting time is more than 7 minutes. 8 (i) No, because correlation does not imply causation / The increase in the monthly sales of refrigerators could be due to other factors such as a rise in the income level.

41 9 (ii) y ($ in thousands) (, 5.) (5,.5) ($ in hundreds) There appears to be a curvilinear/non-linear relationship between and y, thus a linear model is not likely to be appropriate. (iii) (A) r = (to 4dp) (B) r = (to 4dp) Since the r value between e and y has an absolute value closer to, y a be is the better model. (iv) New regression line (8 data points) for y on e is y e y Since e and y lie on the new regression line y on e, and letting m when y., 7 i m e e i Using GC (-var stats), e i e m e m Monthly advertising ependiture = $400 (nearest hundred) i m

42 0 9 (i) Assume that the: weights of the 5 people chosen are independent of each other sample is chosen randomly. (ii) P( X ) P( X ) and P( X ) P( X ) C p( p) C p ( p) and C p ( p) C p ( p) Since ( p) 0 and p 0, p p and p p p p (iii) Since and (shown).965 (from GC) n 5 p, np.965 p 0.9 (iv) X ~ B(5, 0.9) P(( X 4) ( X X )) P( X 4)P( X ) P( X 5)P( X 4) 0.074(0.98) (0.0097)(0.9906) ( sf) 0 (i) Number of ways =! !! (ii) Method I S D R I B U I O N I S D R I B U I O N I S D R I B U I O N There are ways to slot in the T s Total number of ways = total number of ways to arrange the remaining ten letters 0! 84400!

43 Method T T Case : One I included between the two T s! Number of ways = 7 C6 8! 0960! Case : Two I s included between the two T s 8! Number of ways = 7 C6! 84670! Case : Three I s included between the two T s 8! Number of ways = 7 C5! 84670! Total number of ways (iii) Method Case : Both I together but both T separated II D S R B U O N 7 single letters (ecluding Is and Ts) and block of Is. Number of ways = Case : Both T together but I separated 9 Number of ways = 8! C 4550 (same approach as case ) 9 8! C 4550 Case : Both I together and both T together II TT D S R B U O N Number of ways = 9! 6880 Total number of ways in complement = (4550 ) 6880 = 6590 Method 7 single letters (ecluding Is and Ts), block of Is and block of Ts. Number of ways in which both T are together = 0!! Number of ways in which both I are together = 0!! Number of ways in which both pairs of identical letters are together = 9! 0! Total number of ways in complement 9! 6590!

44 6590 Required probability = 0.67!!! (b)(i) P(holder is not involved in any accident the holder is classified as average risk ) 00% 5% 85% 0.85 (ii) Probability of a randomly chosen policy holder not involved in any car accident = (0.)(0.99) + (0.6)(0.85) + (0.)(0.75) 47 = 0.84 or 500 (iii) P(policy holder is low risk has met at least one car accident) P(holder is classified as 'low risk' and met with at least accident) P(holder meets with at least accident) 0.(0.0) (to sf) or 66 (iv) Let C be the cost of insuring a randomly chosen low risk policy holder (in thousands). c P(C = c) 0.99 (0.0) (0.75) = (0.0) (0.5) = (0.0) (0.08) = (0.0) (0.0) = (v) E( C ) = 00(0.000)+50(0.0008)+0(0.005)+5(0.0075)= 0.5 Note: Profit = Premium Charged Cost Incurred for Repair 000(0.5) + 00 =.5 The company should charge $.50 for a car insurance plan for low risk. Alternative (Using Profit = Premium Cost Incurred ) Let P be the premium charged by Adiva for a low risk holder. P(0.99) ( P 5000)(0.0075) ( P 0000)(0.005) ( P 50000)(0.0008) ( P00000)(0.000) 00 Solving, P.5 The company should charge $.50 for a car insurance plan for low risk.