M 362K, Spring 03, Smith

## Assignment for Wednesday, November 19

*To Hand In:*

1. p. 291 #15.

2. p. 292 #22. Be sure to give your reasons. In part (b), be sure to specify
where the marginal density is zero.

3. The number if years a brand A battery lasts is an exponential random
variable X with parameter 1. The number of years that a brand B battery lasts
is an exponential random variable Y with parameter 2. X and Y are independent
random variables.

a. Find the joint pdf of X and Y.

b. Find the probability that a randomly chosen brand A
battery lasts longer than a randomly chosen brand B battery.