# MTH 304 Study Guide - U.S. Route 25E, Quadratic Equation, Standard Deviation

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19 Apr 2013

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1. Suppose that vehicles taking a particular freeway exit can turn right (R), turn left (L), or go straight (S).

Consider observing the direction for each of three successive vehicles.

a. List all outcomes in the event A that all three vehicles go in the same direction.

b. List all outcomes in the event B that all three vehicles take different directions.

c. List all outcomes in the event C that exactly two of the three vehicles turn right.

d. List all outcomes in the even D that exactly tow vehicles go in the same direction.

e. List outcomes in

D

, C D, and C D.

ANSWER:

a. Event A = { RRR, LLL, SSS }

b. Event B = { RLS, RSL, LRS, LSR, SRL, SLR }

c. Event C = { RRL, RRS, RLR, RSE, LRR, SRR }

d. Event D = {RRL, RRS, RLR, RSE, LRR, SRR, LLR, LLS, LRL, LSL, RLL, SLL, SSR, SSL, SRS,

SLS, RSS, LSS}

e. Event

D

contains outcomes where all cars go the same direction, or they all go different directions:

D

= { RRR, LLL, SSS, RLS, RSL, LRS, LSR, SRL, SLR }

Because Event D totally encloses Event C, the compound event C D = D. Therefore, C D = {

RRL, RRS, RLR, RSR, LRR, SRR, LLR, LLS, LRL, LSL, RLL, SLL, SSR, SSL, SRS, SLS, RSS,

LSS }

Using similar reasoning, we see that the compound event CD = C. Therefore, C D = { RRL,

RRS, RLR, RSR, LRR, SRR }

2. A college library has five copies of a certain text on reserve. Two copies (1 and 2) are first printings, and

the other three (3, 4, and 5) are second printings. A student examines these books in random order,

stopping only when a second printing has been selected. One possible outcome is 4, and another is 125.

a. List the S.

b. Let A denote the event that exactly one book must be examined. What outcomes are in A?

c. Let B be the event that book 4 is the one selected. What outcomes are in B?

d. Let C be the event that book 2 is not examined. What outcomes are in C?

ANSWER:

a.

Outcome Number

Outcome

1

123

2

124

3

125

4

213

5

214

6

215

7

13

8

14

9

15

10

23

11

24

12

25

13

3

14

4

15

5

b. Outcome numbers 13, 14, 15, so A={3, 4, 5}

c. Outcome numbers 2, 5, 8, 11, 14 so B={124, 214, 14, 24, 4}

d. Outcome numbers 7, 8, 9, 13, 14, 15 so C={13, 14, 15, 3, 4, 5}

3. A certain sports car comes equipped with either an automatic or a manual transmission, and the car is

available in one of four colors. Relevant probabilities for various combinations of transmission type and

color are given in the accompanying table.

Color

Transmission Type

White

Blue

Black

Red

A

.13

.10

.11

.11

M

.15

.07

.15

.18

Let A = (automatic transmission), B = {black}, and C = {white}.

a. Calculate P(A), P(B), and P(A B).

b. Calculate both P(A|B) and P(B|A), and explain in context what each of these probabilities represents.

c. Calculate and interpret P(A|C) and P(A/

C

).

ANSWER:

a. P(A) = .13 + .10 + .11 + .11 =.45,

P(B) = .11 + .15 = .26

P(A B) = .11

b. P(A|B) =

( ) .11 .4231

( ) .26

P A B

PB

Knowing that the car is black, the probability that it has an automatic transmission is .4231.

P(B|A) =

( ) .11 .2444

( ) .45

P A B

PA

Knowing that the car has an automatic transmission, the probability that it is black is .2444.

c. P(A|C) =

( ) .13 .4643

( ) .28

P A C

PC

The probability that the car has automatic transmission, knowing that the car is white is .4643.

( | )P A C

=

( ) .32 .4444

( ) .72

P A C

PC

Knowing that the car is not white, the probability that it has an automatic transmission is .4444.

4. Consider the following information: where A = {Visa Card}, B = {MasterCard}, P(A) = .5, P(B) = .4, and

P(A B) = .25. Calculate each of the following probabilities.

a. P(B|A)

b. P(

B

|A)

c. P(A|B)

d. P(

A

|B)

e. Given that an individual is selected at random and that he or she has at least one card, what is the

probability that he or she has a Visa card?

ANSWER:

a. P(B|A) =

( ) .25 .50

( ) .50

P A B

PA