Fall 2013 Math Determine whether the lines through the pairs of points A( 3, 2), B(5, 14) and C(3, 2), D( 12, 4) are perpendicular.

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1 Final Exam Answer key Fall 013 Math Determine whether the lines through the pairs of points A( 3, ), B(5, 14) and C(3, ), D( 1, 4) are perpendicular. m 1 = 14 5 ( 3) = 1 8 = 3, m = 4 ( ) 1 3 = 6 15 = 5 1 m 1. They are NOT perpendicular.. Break-Even Analysis A division of the Gibson Corporation manufactures bycycle pumps. Each pump sells for $6, and the variable cost of producing each unit is 60% of the selling price. The monthly fixed costs are $48, 000. What is the break-even point for the division? The cost is $6 (.6) = $3.6 C(x) = 3.6x + 48, 000, R(x) = 6x C(x) = R(x), 3.6x + 48, 000 = 6x, 48, 000 =.4x, x = 0, 000, R(0, 000) = $10, 000 The the break-even operation, the division should manufacture 0, 000 pumps, resulting in a break-even revenue of $10, 000 per month. 3. Using an augmented matrix and the Gauss-Jordan elimination method determine whether the system has a solution and find the solution or solutions, if they exist. (a) x + y + z = 0 x y + z = 9 x + y z = 18 The augmented matrix is R R R /( 3) R R 1 R /( 3) 1 0 / R 1 R 0 1 1/3 3 R 1 3 R R R Answer: x =, y = 1, z = /

2 (b) x y + z = 3 x + y z = 1 y z = The augmented matrix is R R R 3 R R / Answer: The system has no solutions For the system of linear equations x y = x + 3y = 15 (a) write a matrix equation that is equivalent to the system AX = B, where A = [ [ x, X = y [, B = 15 (b) solve the system using an inverse matrix A 1 = X = A 1 B = x = 3, y = 4. [ [ [ = [ = [ = 5. By constructing truth tables prove De Morgan s Law (p q) p q. Truth table: p q p q (p q) p q p q T T T F F F F T F T F F T F F T T F T F F F F F T T T T The fourth and seventh columns are equivalent. Hence, De Morgan s Law is true. Page

3 6. Determine whether the argument is valid. p q p q p q Truth table: p q p q p q p q p q T T F F T T F T F F T F T T F T T F F F F F F T T F T F The entries in the first row are both true, but the corresponding entry for the conclusion is false. Therefore, the argument is invalid.. How many days will it take for a sum of $500 to earn $30 interest if it is deposited in a bank paying ordinary simple interest at the rate of 6% per year? (Use a 365-day year.) 6% per year equals % = per day. Let the number of days be x. Then x = 30, x = = 3 days Loan Amortization A sum of $5, 000 is to be repaid over a 6-year period trough equal installments made at the end of each year. If an interest rate of 9% per year is charged on the unpaid balance and interest calculations are made at the end of each year, determine the size of each installment so that the loan (principal plus interest charges) is amortized at the end of 6 years. P = 5, 000, i = r =.09, n = 6 R = (5, 000)(.09), R = $ (1.09) 6 9. Find the sum of the first seventeen terms of the arithmetic progression whose fourth and eleventh terms are 14 and 35, respectively. a n = a + (n 1)d, a 4 = a + 3d = 14, a 1 1 = a + 10d = 35. Then a = 5, d = 3. S n = n (a + (n 1)d), S 1 = 1 ( 5 + (1 1) 3) = 493. Page 3

4 10. Let U = {, 4, 6, 8, 10, 1, 14, 16, 18}, A = {4, 6, 8, 10}, B = {, 6, 10, 14, 18}, C = {4, 6, 10, 1, 18}. List the elements of the sets (a) (A B C) c A B C = {, 4, 6, 8, 10, 1, 14, 18}, (A B C) c = {16} (b) (A B C) c A B C = {6, 10}, (A B C) c = {, 4, 8, 1, 14, 16, 18} (c) A c (B C) B C = {, 4, 6, 10, 1, 14, 18}, A c = {, 1, 14, 16, 18}, A c (B C) = {, 1, 14, 18} 11. A company car that has a seating capacity of seven is to be used by seven empoloyees who have formed a car pool. If only three of these employees can drive, how many possible seating arrangements are there for the group? P (3, 3) P (4, 4) = 3! 4! = 6 4 = Let S = {s 1, s, s 3, s 4, s 5 } be the sample space associated with an experiment and A = {s, s 3, s 4 }, B = {s, s 5 }. The probability distribution of the experiment is shown in the following table: Outcome s 1 s s 3 s 4 s 5 Probability Find (a) P (A) P (A) = P (s ) + P (s 3 ) + P (s 4 ) = =.6 (b) P (A B) A B = {s }, P (A B) = P (s ) =. Page 4

5 (c) P (A B c ) B c = {s 1, s 3, s 4 }, A B c = {s 1, s, s 3, s 4 }, P (A B c ) = P (s 1 ) + P (s ) + P (s 3 ) + P (s 4 ) = =. 13. Urn A contains five green balls and five blue balls. Urn B contains three green balls and four blue balls. A ball is drawn from urn A and then trasferred to Urn B. A ball is then drawn from Urn B. What is the probability that the transferred ball was green given that the second ball drawn was blue. Let A denote the event that the transferred ball was green and B denote the event that a ball is then drawn from Urn B was blue. We need to find the conditional probability P (A B). By Bayes Theorem P (A B) = P (A) P (B A) P (A) P (B A) + P (A c ) P (B A c ) P (A) = 1, P (B A) = 1, P (Ac ) = 1, P (B Ac ) = 5 8 P (A B) = = 4 9 = An experiment consists of two independent trials. The outcomes of the first trial are A and B with probabilities of occuring equal to.3 and. respectively. The outcomes of the second trial are C and D with probabilities of occuring equal to.8 and. respectively. Draw a tree diagram representing this experiment and use it to find: (a) P (B C) P (B C) = P (B) P (C B) = (.)(.8) =.56 (b) P (D A) P (D A) =. (c) Are A and C independent events? Yes. 15. An exam consists of eight true-or-false questions. If a student guesses at every answer, what is the probability that he or she will answer exactly three questions correctly? Page 5

6 C(8, 3) 8 = = 5 = 3 = Driving Age Requirements The minimum age requirement for a regular driver s license differs from state to state. The frequency distribution for this age requirement in the 50 states given in the following table: Table 1: Driving Age Requirement Distribution Minimum Age Frequency of Occurence (a) Describe a random variable X that is associated with these data. X is a minimum driving age requirement in different states. (b) Find the probability distribution for the random variable X Table : Driving Age Requirement Probability Distribution x P (X = x) (c) Compute mean, variance, and standard deviation of X µ = 15(.04) + 16(.8) + 1(.06) + 18(.5) + 19(.06) + 1(.04) = 1.44, Var(X) = , σ = = If the probability that a certain tennis player will serve an ace is., what is the probability that she will serve exactly three aces out of seven serves? (Assume that the seven serves are independent). p = C(, 3)(.) 3 (.8) 4 = Let Z be the standard normal random variable. (a) Find the probability P (0.3 < Z < 1.64) Take data from the provided table. P (0.3 < Z < 1.64) = P (Z < 1.64) P (Z < 0.3) = = Page 6

7 (b) Find the value of z if z satisfies the condition P (Z < z) = z =.48 Page

8 The Standard Normal Distribution z Page 8

9 19. The tread lives of the Super Titan radial tires under normal driving conditions are normally distributed with a mean of 35, 000 mi and a standard deviation of 305 mi. What is the probability that a tire selected at random will have a tread life of less than 40, 000 mi? P (X < 40, 000) = P ( Z < ) 40, , 000 = P (Z < 1.56) = A charitable organization estimates that in a certain community 80% of the people who make a donation this year will make a donation next year. It also estimates that 30% of the people who do not make a donation this year will make a donation next year. (a) Find the transition matrix corresponding to this situation. T = [ (b) Suppose that this year 40% of the people made a donation. What is the initial distribution matrix? X 0 = [ (c) What percentage of the people is expected to donate next year? X 1 = T X 0 = [ [ = [ (d) What percentage of the people is expected to donate in the long run? T X = X, where X = [ x y.8x +.3y = x.x +.y = y x + y = 1 [ 60 X = 40.x +.3y = 0.x.3y = 0 x + y = 1 x 3y = 0 x + y = 1 y = 3 ( x x = 3 5 = 60% ) x = 1 y = 5 = 40% Page 9