*Questions 15 – 17 refer to the following:* The average lifetime of a certain new cell phone is 3 years. The manufacturer will replace any cell phone failing within 2 years of the date of purchase. The lifetime of these cell phones is known to follow an exponential distribution.

### Exercise 15

The decay rate is

**A.**0.3333**B.**0.5000**C.**2.0000**D.**3.0000

#### Solution

A

### Exercise 16

What is the probability that a phone will fail within 2 years of the data of purchase?

**A.**0.8647**B.**0.4866**C.**0.2212**d.**0.9997

#### Solution

B

### Exercise 17

What is the median lifetime of these phones (in years)?

**A.**0.1941**B.**1.3863**C.**2.0794**D.**5.5452

#### Solution

C

*Questions 18 – 20 refer to the following:* The Sky Train from the terminal to the rental car and long term parking center is supposed to arrive every 8 minutes. The waiting times for the train are known to follow a uniform distribution.

### Exercise 18

What is the average waiting time (in minutes)?

**A.**0.0000**B.**2.0000**C.**3.0000**D.**4.0000

#### Solution

D

### Exercise 19

Find the 30th percentile for the waiting times (in minutes).

**A.**2.0000**B.**2.4000**C.**2.750**D.**3.000

#### Solution

B

### Exercise 20

The probability of waiting more than 7 minutes given a person has waited more than 4 minutes is?

**A.**0.1250**B.**0.2500**C.**0.5000**D.**0.7500

#### Solution

B