Statistics Test 2a Prof. VanderHoff Spring 2003

All work must be shown on exam to receive credit.

1. [6] Calculate the mean and standard deviation for the random variable X:

X prob

1	0.1
3	0.3
5	0.6

2. [8] Calculate the probability that you find a parking place within 5 minutes on 3 days during the week. You travel to campus 5 days a week and the probability of finding a parking place within 5 minutes is1/3.

3. [5] Calculate the probability that you wait on the phone from between 3 and 10 minutes. The distribution of waiting time is uniform with a minimum value of 0 and a maximum value of 20 minutes.

4. [8] Calculate the probability of having a sample proportion between .33 and.38 from a sample of 400. The population proportion is .4.

5. [6] What size sample is required in order to have a maximum error of 1 with a 95% confidence level when the population standard deviation=2.

6. [6] Calculate the following probabilities from a distribution with the probability of success=.4 and the number of trials=12.

The number of successes=6

The number of successes is between 8 and 9 inclusive

7 [11] Calculate the 99% confidence interval for the population mean. A sample of 81 had a sample mean=22 and standard deviation=6.

8. [8] Calculate the probability that the class average test score is between 75 and 79. The number of students taking the exam is 81 and the test score mean=73 and the standard deviation=20.

9. [16] Calculate the 95% confidence interval for the population mean using the following data:

X

3

7

9

0

-1

6

10. [8] The mean price of purchases is $150 and the standard deviation=$10. What is the probability of a purchase exceeding $145?

11. [11] Calculate the 95% confidence interval for the population proportion of Bush supporters. A sample of 100 students indicates 85 support Bush.

12 [5] The time spent studying for stats has a mean=30 and a standard deviation=4. What is the value of time studying that only 2.5 % of students will exceed?