1. A discrete random variable can assume 4 possible values, as listed in the accompanying probability distribution.

x:	-5	0	2	5
p(x):	0.20	0.30		0.10

a) Find p(2).

2. A discrete random variable can assume 4 possible values, as listed in the accompanying probability distribution.

x:	-5	0	2	5
p(x):	0.20	0.30		0.10

(b) Find the mean of x.

3. A discrete random variable can assume 4 possible values, as listed in the accompanying probability distribution.

x:	-5	0	2	5
p(x):	0.20	0.30		0.10

(c) Find the variance of x.

4. A manufacturing process that produces electron tubes is known to have a 10% defective rate. Suppose a

random sample of 15 tubes is selected from the manufacturing process.

a) Find the probability that no more than two defectives are found?

5. A manufacturing process that produces electron tubes is known to have a 10% defective rate. Suppose a

random sample of 15 tubes is selected from the manufacturing process.

b) Find the probability that exactlyfourdefectives are found?

6. A manufacturing process that produces electron tubes is known to have a 10% defective rate. Suppose a

random sample of 15 tubes is selected from the manufacturing process.

c) Find the probability that at leastthreedefectives are found?

7. A television cable company receives numerous phone calls throughout the day from customers reporting service troubles and from would-be subscribers to the cable network. Most of these callers are put "on hold" until a company operator is free to help them. The company has determined that the length of time a caller is on hold is normally distributed with a mean of 3.1 minutes and a s.d of 0.9 minute.

What percentage of company's callers are put on hold for at least 4.8 minutes?

8. Water availability is of prime importance in the life cycle of most reptiles. To determine the rate of evaporative water loss of a certain species of lizard at a particular desert site, 34 such lizards were randomly collected, weighed and placed under the appropriate experimental conditions. After 24 hours, each lizard was removed, weighed, and its total water loss was calculated by subtracting its body weight after treatment from its initial body weight. Previous studies have shown that the relative frequency distribution of water loss for this species of lizard has a mean of 3.1 grams and a s.d. of 0.8 gram.

a) What is the approximate sampling distribution of x , the mean water loss of the 34 lizards

9. Water availability is of prime importance in the life cycle of most reptiles. To determine the rate of evaporative water loss of a certain species of lizard at a particular desert site, 34 such lizards were randomly collected, weighed and placed under the appropriate experimental conditions. After 24 hours, each lizard was removed, weighed, and its total water loss was calculated by subtracting its body weight after treatment from its initial body weight. Previous studies have shown that the relative frequency distribution of water loss for this species of lizard has a mean of 3.1 grams and a s.d. of 0.8 gram

b) What is the probability that x is less than 2.7 grams?

10. A psychologist is studying the effects of lack of sleep on the performance of various perceptual-motor tasks. After a given period of sleep deprivation, a measurement of reaction time to an auditory stimulus was taken for each of 36 adult male subjects.

The reaction times (in seconds) are summarized as follows:x= 1.82, S=0.22.

Find a 99% confidence interval for the mean reaction time for sleep-deprived male subjects.