EBook Problems Distrib RV

EBook Problems Set - Random Variables

Problem 1

The probability model below describes the number of repair calls that an appliance repair shop may receive during an hour:

Repair calls	0	1	2	3
P(x)	0.1	0.3	0.4	0.2

The probability that the number of repair calls is at least 2 is:

• Choose one answer.

(a) 0.8

(b) 0.2

(c) 0.4

(d) 0.6

Answer

 (d)

Problem 2

In a litter of seven kittens, three are female. You pick two kittens at random. The probability model for the number of male kittens is:

Number males	0	1	2
Probability	0.143	0.571	0.286

The expected number of males is:

• Choose one answer.

(a) 0.64

(b) 1.7

(c) 1.14

(d) 2.1

Answer

 (c)

Problem 3

Let X represent a discrete random variable that takes any of the values and probabilities given below:

X	-2	5	6
P(X)	0.4	0.4	__

The probability for X = 6 is missing. What is it?

• Choose one answer.

(a) It cannot be determined from the information given

(b) 0.2

(c) 0.6

(d) 2.3

Answer

 (b)

Problem 4

The manager of a stock room in a factory knows from her study of records that the daily demand for a certain tool has the following probability model:

Demand	0	1	2
Probability	0.1	0.5	0.4

Suppose it costs the factory $10 each time the tool is used. Find the variance of the daily cost of using the tool.

• Choose one answer.

(a) 13

(b) 41

(c) 1.3

(d) 10

Answer

 (b)

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