1. (Updated on 11/30/2011 3:29 PM) The average weight of 60 randomly selected compact automobiles was 2627 pounds. The
population standard deviation was 400 pounds.
a) Find the best point estimate of the true mean weight of the automobiles.
b) Find the 99% confidence interval of the true mean weight of the automobiles.
2. The average diastolic blood pressure of a certain age group of people is 85 mm Hg. The population standard deviation is 6. Assume the variable is normally distributed.
a. If an individual from this age group is selected, find the probability that his or her pressure is greater than 90.
b. If 15 people from this age group are selected, find the probability that the sample mean is greater than 90.
c. If 15 people from this age group are selected, find the probability that the sample mean is above 80.
3. A recent study of 25 commuters showed that they spent an average of $18.23 on public transportation per week. The standard deviation of the sample was $3.00. Find the 95% confidence interval of the true mean.
4. A researcher is interested in estimating the average salary of teachers in a large urban school district. She wants to be 95% confident that her estimate is correct. If the population standard deviation is $1050, how large a sample is needed to be accurate within $100?
5. The state’s education secretary claims that the average cost of one year’s tuition for all private high schools in the state is $2350. A sample of 30 private high schools is selected, and the average tuition is $2315. The standard deviation for the population is $38. At 
= 0.05, is there enough evidence to reject the claim that the average cost of tuition is equal to $2350? Use p-value method.
6. A large hospital instituted a fitness program to reduce absenteeism. The
director reported that the average number of working hours lost due to illness
per employee is 48 hours per year. After one year, a sample of 18 employees showed an average of 41 hours of work lost, with a
sample standard deviation of 5. The Director claimed that the program reduces absenteeism. Test his hypothesis at =0.10.
7. The manager of a large factory believes that the average hourly wage of the employees is below $9.78 per hour. A sample of 18 employees has a mean hourly wage of $9.60. The standard deviation of all salaries is $1.42. Assume the variable is normally distributed. At = 0.1, is there enough evidence to support the manager’s claim?