General Certificate of Education Advanced Subsidiary Examination January 2010

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1 General Certificate of Education Advanced Subsidiary Examination January 2010 Mathematics Unit Statistics 1B Statistics Unit Statistics 1B Wednesday 13 January pm to 3.00 pm MS/SS1B For this paper you must have: an 8-page answer book the blue AQA booklet of formulae and statistical tables an insert for use in Question 7 (enclosed). You may use a graphics calculator. Time allowed 1 hour 30 minutes Instructions Use black ink or black ball-point pen. Pencil should only be used for drawing. Write the information required on the front of your answer book. The Examining Body for this paper is AQA. The Paper Reference is MS/SS1B. Answer all questions. Show all necessary working; otherwise marks for method may be lost. The final answer to questions requiring the use of tables or calculators should normally be given to three significant figures. Fill in the boxes at the top of the insert. Information The marks for questions are shown in brackets. The maximum mark for this paper is 75. Unit Statistics 1B has a written paper only. Advice Unless stated otherwise, you may quote formulae, without proof, from the booklet. P20793/Jan10/MS/SS1B 6/6/6/ MS/SS1B

2 2 Answer all questions. 1 Draught excluder for doors and windows is sold in rolls of nominal length 10 metres. The actual length, X metres, of draught excluder on a roll may be modelled by a normal distribution with mean 10.2 and standard deviation (a) Determine: (i) PðX<10:5Þ ; (3 marks) (ii) Pð10:0 <X< 10:5Þ. (3 marks) (b) A customer randomly selects six 10-metre rolls of the draught excluder. Calculate the probability that all six rolls selected contain more than 10 metres of draught excluder. (3 marks) 2 Lizzie, the receptionist at a dental practice, was asked to keep a weekly record of the number of patients who failed to turn up for an appointment. Her records for the first 15 weeks were as follows a b Unfortunately, Lizzie forgot to record the actual values for two of the 15 weeks, so she recorded them as a and b. However, she did remember that a<10 and that b>40. (a) Calculate the median and the interquartile range of these 15 values. (4 marks) (b) Give a reason why, for these data: (i) the mode is not an appropriate measure of average; (ii) the standard deviation cannot be used as a measure of spread. (2 marks) (c) Subsequent investigations revealed that the missing values were 8 and 43. Calculate the mean and the standard deviation of the 15 values. (2 marks) P20793/Jan10/MS/SS1B

3 3 3 The table shows, for each of a random sample of 7 weeks, the number of customers, x, who purchased fuel from a filling station, together with the total volume, y litres, of fuel purchased by these customers. x y (a) Calculate the equation of the least squares regression line of y on x. (4 marks) (b) (c) Estimate the volume of fuel sold during a week in which 200 customers purchase fuel. (2 marks) Comment on the likely reliability of your estimate in part (b), given that, for the regression line calculated in part (a), the values of the 7 residuals lie between approximately 415 litres and þ430 litres. (2 marks) 4 Each school-day morning, three students, Rita, Said and Ting, travel independently from their homes to the same school by one of three methods: walk, cycle or bus. The table shows the probabilities of their independent daily choices. Walk Cycle Bus Rita Said Ting (a) Calculate the probability that, on any given school-day morning: (i) all 3 students walk to school; (2 marks) (ii) only Rita travels by bus to school; (2 marks) (iii) at least 2 of the 3 students cycle to school. (4 marks) (b) Ursula, a friend of Rita, never travels to school by bus. The probability that: Ursula walks to school when Rita walks to school is 0.9 ; Ursula cycles to school when Rita cycles to school is 0.7. Calculate the probability that, on any given school-day morning, Rita and Ursula travel to school by: (i) the same method; (3 marks) (ii) different methods. (1 mark) P20793/Jan10/MS/SS1B Turn over s

4 4 5 In a random sample of 12 bags of flour, the weight, in grams, of flour in each bag was recorded as follows (a) It may be assumed that the weight of flour in a bag is normally distributed with a standard deviation of 10.5 grams. (i) (ii) (iii) Construct a 98% confidence interval for the mean weight, m grams, of flour in a bag, giving the limits to four significant figures. (5 marks) State why, in constructing your confidence interval, use of the Central Limit Theorem was not necessary. (1 mark) If the distribution of the weight of flour in a bag was unknown, indicate a minimum number of weights that you would consider necessary for a confidence interval for m to be valid. (1 mark) (b) The statement 1 kg is printed on each bag. Comment on this statement using both the confidence interval that you constructed in part (a)(i) and the weights of the given sample of 12 bags. (3 marks) (c) Given that m ¼ 1000, state the probability that a 98% confidence interval for m will not contain (1 mark) P20793/Jan10/MS/SS1B

5 5 6 During the winter, the probability that Barry s cat, Sylvester, chooses to stay outside all night is 0.35, and the cat s choice is independent from night to night. (a) Determine the probability that, during a period of 2 weeks (14 nights) in winter, Sylvester chooses to stay outside: (i) on at most 7 nights; (2 marks) (ii) on at least 11 nights; (2 marks) (iii) on more than 5 nights but fewer than 10 nights. (3 marks) (b) (c) Calculate the probability that, during a period of 3 weeks in winter, Sylvester chooses to stay outside on exactly 4 nights. (3 marks) Barry claims that, during the summer, the number of nights per week, S, on which Sylvester chooses to stay outside can be modelled by a binomial distribution with n ¼ 7 and p ¼ 5 7. (i) Assuming that Barry s claim is correct, find the mean and the variance of S. (2 marks) (ii) For a period of 13 weeks during the summer, the number of nights per week on which Sylvester chose to stay outside had a mean of 5 and a variance of 1.5. Comment on Barry s claim. (2 marks) Turn over for the next question P20793/Jan10/MS/SS1B Turn over s

6 6 7 [Figure 1, printed on the insert, is provided for use in this question.] Harold considers himself to be an expert in assessing the auction value of antiques. He regularly visits car boot sales to buy items that he then sells at his local auction rooms. Harold s father, Albert, who is not convinced of his son s expertise, collects the following data from a random sample of 12 items bought by Harold. Item Purchase price ( x) Auction price ( y) A B C D E F G H I J K L (a) Calculate the value of the product moment correlation coefficient between x and y. (3 marks) (b) Interpret your value in the context of this question. (2 marks) (c) (i) On Figure 1, complete the scatter diagram for these data. (3 marks) (ii) Comment on what this reveals. (2 marks) (d) When items J and L are omitted from the data, it is found that S xx ¼ 4854:4 S yy ¼ 4216:1 S xy ¼ 4268:8 (i) Calculate the value of the product moment correlation coefficient between x and y for the remaining 10 items. (2 marks) (ii) Hence revise as necessary your interpretation in part (b). (1 mark) END OF QUESTIONS P20793/Jan10/MS/SS1B

7 Centre Number Candidate Number Surname Other Names Candidate Signature General Certificate of Education Advanced Subsidiary Examination January 2010 Mathematics MS/SS1B Unit Statistics 1B Statistics Unit Statistics 1B Insert Instructions Insert for use in Question 7. Fill in the boxes at the top of this page. Fasten this insert securely to your answer book at the end of the examination. Turn over for Figure 1 P20793/Jan10/MS/SS1B 6/6/6/ Turn over s

8 2 Figure 1 (for use in Question 7) y ~ Prices of Antiques Auction price ( ) A C B E D F Purchase price ( ) ~ x Copyright Ó 2010 AQA and its licensors. All rights reserved. P20793/Jan10/MS/SS1B

9 Version 1.0: 0110 klm General Certificate of Education Mathematics 6360 Statistics 6380 MS/SS1B/W Statistics 1B Mark Scheme 2010 examination - January series

10 Mark schemes are prepared by the Principal Examiner and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation meeting attended by all examiners and is the scheme which was used by them in this examination. The standardisation meeting ensures that the mark scheme covers the candidates responses to questions and that every examiner understands and applies it in the same correct way. As preparation for the standardisation meeting each examiner analyses a number of candidates scripts: alternative answers not already covered by the mark scheme are discussed at the meeting and legislated for. If, after this meeting, examiners encounter unusual answers which have not been discussed at the meeting they are required to refer these to the Principal Examiner. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of candidates reactions to a particular paper. Assumptions about future mark schemes on the basis of one year s document should be avoided; whilst the guiding principles of assessment remain constant, details will change, depending on the content of a particular examination paper. Further copies of this Mark Scheme are available to download from the AQA Website: Copyright 2010 AQA and its licensors. All rights reserved. COPYRIGHT AQA retains the copyright on all its publications. However, registered centres for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to centres to photocopy any material that is acknowledged to a third party even for internal use within the centre. Set and published by the Assessment and Qualifications Alliance. The Assessment and Qualifications Alliance (AQA) is a company limited by guarantee registered in England and Wales (company number ) and a registered charity (registered charity number ). Registered address: AQA, Devas Street, Manchester M15 6EX Dr Michael Cresswell Director General 2

11 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series Key to mark scheme and abbreviations used in marking M m or dm A B E mark is for method mark is dependent on one or more M marks and is for method mark is dependent on M or m marks and is for accuracy mark is independent of M or m marks and is for method and accuracy mark is for explanation or ft or F follow through from previous incorrect result MC mis-copy CAO correct answer only MR mis-read CSO correct solution only RA required accuracy AWFW anything which falls within FW further work AWRT anything which rounds to ISW ignore subsequent work ACF any correct form FIW from incorrect work AG answer given BOD given benefit of doubt SC special case WR work replaced by candidate OE or equivalent FB formulae book A2,1 2 or 1 (or 0) accuracy marks NOS not on scheme x EE deduct x marks for each error G graph NMS no method shown c candidate PI possibly implied sf significant figure(s) SCA substantially correct approach dp decimal place(s) No Method Shown Where the question specifically requires a particular method to be used, we must usually see evidence of use of this method for any marks to be awarded. However, there are situations in some units where part marks would be appropriate, particularly when similar techniques are involved. Your Principal Examiner will alert you to these and details will be provided on the mark scheme. Where the answer can be reasonably obtained without showing working and it is very unlikely that the correct answer can be obtained by using an incorrect method, we must award full marks. However, the obvious penalty to candidates showing no working is that incorrect answers, however close, earn no marks. Where a question asks the candidate to state or write down a result, no method need be shown for full marks. Where the permitted calculator has functions which reasonably allow the solution of the question directly, the correct answer without working earns full marks, unless it is given to less than the degree of accuracy accepted in the mark scheme, when it gains no marks. Otherwise we require evidence of a correct method for any marks to be awarded. 3

12 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series MS/SS1B Q Solution Marks Total Comments 1(a)(i) X ~ N(10.2, ) ( X. ) P < 10 5 = P Z < 015. M1 Standardising (10.45, 10.5 or 10.55) with 10.2 and ( 015., 0.15 or ) and/or (10.2 x) = P(Z < 2) A1 CAO; ignore inequality and sign May be implied by a correct answer = A1 3 AWRT ( ) (ii) P100 (. < X < 105. ) = [C s (a)(i)] P( X < 10. 0) M1 Or equivalent; must be clear correct method if answer incorrect and answer > 0 = (a)(i) P( Z 133. ) < Method correct using 1.3 gives 0.88 to = (a)(i) (1 p) M1 m1 A0 = ( ) m1 Area change May be implied by a correct answer or answer > 0.5 = to A1 3 AWFW ( ) M1 m1 A1 for [1 (a)(i)] = M1 m0 A0 for (a)(i) = M0 mo A0 for answer < 0 (b) P(X > 10) = p[from (a)(ii)] = to B1F Correct value or F on value used or implied in (a)(ii) providing > 0.5 Use of 1.3 gives P(6 rolls > 10) = M1 Accept any probability to power to A1 3 AWFW Note: B0F M1 A0 is possible Total 9 4

13 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series MS/SS1B (cont) Q Solution Marks Total Comments 2(a) Ordering values gives: (a) (b) M1 May be implied by correct median or correct IQR Ignore any reference to a and b Median = 26 A1 CAO IQR = = 16 A2 CAO Special Case: Identification that LQ = 18 and UQ = 34 (A1) 4 Both CAO (b)(i) Two values (25 and 37) of mode No unique value Sparse data Many different values B1 Or equivalent (ii) a and b (two values) unknown Impossible to calculate Cannot be calculated B1 2 Or equivalent (c) Mean = x n = = 26 B1 CAO If not identified, assume order is x then s = 9.4 to 9.8 B1 2 SD ( x 2 = 11472) AWFW (9.423 & 9.754) Treat rounding of a correct stated answer to an integer as ISW Special Case: Evidence of x 15 (M1) Total 8 Can only be awarded if no marks scored elsewhere in (c) 5

14 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series MS/SS1B (cont) Q Solution Marks Total Comments 3(a) b (gradient) = 7.05 B2 AWRT ( ) b (gradient) = 7(.00) to 7.1(0) (B1) AWFW Treat rounding of correct stated answers as ISW a (intercept) = 2500 to 2502 B2 4 AWFW ( ) a (intercept) = 2490 to 2510 (B1) AWFW or Attempt at 2 x x y & xy or Attempt at S xx & xy 2 ( y ) S ( S yy ) (M1) & ( ) (all 4 attempted) 7304 & ( ) (both attempted) Attempt at correct formula for b (gradient) (m1) b (gradient) = 7.05 (A1) AWRT a (intercept) = 2500 to 2502 (A1) AWFW Accept a & b interchanged only if identified correctly by a clearly shown equation (stated answers are not sufficient) in (b) If a and b are not identified anywhere in solution, then: 7.05 B to 2502 B1 (b) y 200 = a + b 200 M1 Used May be implied by correct answer = 3890 to 3930 A1 2 AWFW ( ) (c) Large residuals / residual range suggest estimate may be unreliable or Largest residuals only small in relation to y-values (10%) so estimate may be reliable (unreliable) B1 B1dep B1 B1dep 2 (unreliable) requires (10% or equivalent) Special Case: If B0 B0dep then: Involves interpolation Does not involve extrapolation Within observed range (B1) Any one; or equivalent Total 8 6

15 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series MS/SS1B (cont) Q Solution Marks Total Comments Ratios (eg 65:1000) are only penalised by 1 mark at first correct answer 4(a)(i) P(all 3 walk) = M1 Can be implied by correct answer = 65/1000 = 13/200 = A1 2 CAO; do not confuse with 0.65 (ii) P(Rita by bus) = 0.25 (1 0.15) (1 0.20) M1 Can be implied by correct answer = 17/100 = 0.17 A1 2 CAO (iii) P(2 cycle) = ( ) = ( ) 0.55 = ( ) = ( ) B1 CAO at least 1 of these 3 terms or equivalent but allow a 3 P(3 cycle) = = B1 CAO P( 2 cycle) = P(2 cycle) + P(3 cycle) M1 Sum of 4 or 7 terms each a product of 3 probabilities but not 3 = A1 4 CAO or P(0 cycle) = = (B1) CAO P(1 cycles) = = = (B1) ( ) = P( 2 cycle) = 1 [P(0 cycle) + P(1 cycles)] (M1) CAO at least 1 of these 3 terms but allow a 3 1 [sum of 4 terms each a product of 3 probabilities but not 3 ] = (A1) CAO (b)(i) P(WW) = ( ) = P(CC) = ( ) = B1 CAO either P(WW or CC) = M1 Sum of 2 terms each a product of 2 probabilities = A1 3 CAO; or equivalent (ii) P(different) = 1 (b)(i) = B1F 1 F on (b)(i) providing 0 < p < 1 Total 12 7

16 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series MS/SS1B (cont) Q Solution Marks Total Comments 5(a)(i) Mean = = 1010 B1 CAO 98% (0.98) z = 2.32 to 2.33 B1 AWFW (2.3263) σ CI for μ is x ± z M1 n Used Must have n with n > 1 Thus ± A1F F on x and z only Hence 1010 ± (7(.0) to 7.1) or (1003, 1017) A1dep 5 CAO & AWFW (accept 7) Dependent on A1F AWRT Notes: Use of t 11 ( 099. ) = maximum of B1 B0 M1 A0F A0 Use of a corrected 10.5 maximum of B1 B1 M1 A0F A0 (ii) Weight of flour in a bag (may be assumed to be) is normally distributed B1 1 Or equivalent; must refer to weight (iii) Any number such that 20 number 50 B1 1 Must be a single integer value Ignore any reasoning (b) 1 kg or 1000 grams is outside / below CI or From CI, (population) mean weight is greater than 1kg or 1000 grams 3 or 3/12 or 25% of bags in sample weigh less than 1kg or 1000 grams B1F B1 Or equivalent F on (a)(i) Any reference to 1010 B0F Or equivalent; but not some Statement appears dubious/incorrect/invalid B1dep 3 Dependent on both B1F and B1 (c) 2/100 or 1/50 or 0.02 or 2% B1 1 CAO; not 0.02% Total 11 8

17 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series MS/SS1B (cont) Q Solution Marks Total Comments 6(a)(i) R ~ B(14, 0.35) M1 Used somewhere in (a); may be implied P(R 7) = to A1 2 AWFW ( ) (ii) P(R 11) = 1 P(R 10) = 1 ( or ) M1 Requires 1 and 4 dp accuracy = A1 2 AWRT ( ) (iii) P(5 < R < 10) = or (p 1 ) M1 Accept 3 dp accuracy p 2 p 1 M0 M0 A0 (1 p 2 ) p 1 M0 M0 A0 p 1 (1 p 2 ) M1 M0 A0 only providing result > 0 minus or (p 2 ) M1 Accept 3 dp accuracy = to A1 3 AWFW ( ) or B(14, 0.35) expressions stated for at least 3 terms within 4 R 11 gives (M1) Can be implied by correct answer probability = to (A2) AWFW ( ) (b) R ~ B(21, 0.35) M1 Implied from correct stated formula; do not accept misreads Can be implied by a correct answer A1 4 Ignore any additional terms = to A1 3 AWFW ( ) P(R = 4) = (. ) (. ) (c)(i) S ~ B(7, 5/7) Mean = np = 7 5/7 = 5 B1 CAO If not identified, assume order is μ then σ 2 Variance = np(1 p) = 7 5/7 2/7 = 10/7 or 1.42 to 1.43 B1 2 Must clearly state variance value if standard deviation (also) stated CAO / AWFW (ii) Means are the same and (both comparisons clearly stated) Variances/standard deviations are similar Do not accept statements involving correct/incorrect/exact/etc B1dep Must have scored B1 B1 in (i) or B1 B0 plus 10/7 v 1.5 or 10 / 7 v 1.5 stated Barry s claim appears/is sound/valid/correct/likely B1dep 2 Must have scored previous B1dep Total 14 9

18 MS/SS1B/W - AQA GCE Mark Scheme 2010 January series MS/SS1B (cont) Q Solution Marks Total Comments 7(a) r = to B3 3 AWFW ( ) r = to (B2) AWFW r = 0.04 to (B1) AWFW or Attempt at or Attempt at x xy 2 x y S xx S yy & S xy 2 y & (M1) &38605 (all 5 attempted) & 509 (all 3 attempted) Attempt at substitution into correct corresponding formula for r (m1) r = to (A1) AWFW (b) Almost/virtually/practically no / zero (linear) correlation / relationship / association / link (but not no trend ) B1dep Dependent on 0.1 < r < 0.1 Or equivalent; must qualify strength as zero ; B0dep for very weak/weak/etc unless then qualified correctly between purchase and auction prices of antiques B1 2 Context; providing 1 < r < 1 (c)(i) Figure 1: 6 correct labelled points 5 or 4 correct labelled points 3 correct labelled points B3 (B2) (B1) 3 Deduct 1 mark if > 1 point not labelled or labelled incorrectly (ii) (Two) outlier/anomaly/unusual or identification of J and L B1 Or equivalent (Otherwise) a positive/linear correlation B1 2 Or equivalent; ignore any qualification of strength (d)(i) r = M1 Used Award B2 for a correct answer without/with different method r = to A1 2 AWFW ( ) (ii) Very strong/strong positive (linear) correlation/relationship/association/link Previous calculation of r was not appropriate (due to outliers) B1dep (B1) 1 Total 13 TOTAL 75 Dependent on 0.9 < r < 1 Or equivalent; must qualify strength and indicate positive; B0dep for high/etc 10

19 Scaled mark component grade boundaries - January 2010 exams klm A2 units (legacy) Component Maximum Scaled Mark Grade Boundaries Code Component Title Scaled Mark A B C D E SC5W GCE SOCIOLOGY UNIT 5 WRITTEN SCY6 GCE SOCIOLOGY UNIT SP04 GCE SPANISH UNIT SP5W GCE SPANISH UNIT 5 WRITTEN SP6T GCE SPANISH UNIT 6 CENTRE ORAL PED4 GCE SPORT & PE UNIT PED5 GCE SPORT & PE UNIT MS/SS1A/W GCE STATISTICS UNIT 1A WRITTEN MS/SS1A/C GCE STATISTICS UNIT 1A CWK SS1B GCE STATISTICS UNIT 1B SS02 GCE STATISTICS UNIT SS03 GCE STATISTICS UNIT SS04 GCE STATISTICS UNIT Version March 2010 Copyright 2010 AQA and its licensors. All rights reserved. The Assessment and Qualifications Alliance (AQA) is a company limited by guarantee registered in England and Wales (company number ) and a registered charity (registered charity number ). Registered address: AQA, Devas Street, Manchester M15 6EX. Dr Michael Cresswell, Director General.