Statistics

Statistics

A.5 Homework Set: Probability Distributions

1. A study of 32 English composition professors showed that they spent, on average, 74.22 minutes correcting a student’s term paper. Assume the standard deviation is 23.44 and the margin of error is E=8.12.

a. Find the 95% confidence interval of the mean time for all composition papers.

b. If a professor stated that he spent, on average 130 minutes correcting a term paper, what would be your reaction?

2. A study found that 8- to 12- year olds spend an average of $2.86 per day on in-app cell phone purchases. If a sample of 25 children was used, find the 90% confidence interval of the mean. Assume the standard deviation of the sample is $0.15

3. In a sample of 20 customers at the movie theatre, the mean waiting time to order popcorn is 95 seconds. The standard deviation is 21 seconds. Assume that the wait times are normally distributed and construct a 90% confidence interval for the mean wait time of all customers.

4. A sample of 500 nursing applications included 60 frommen. Find the 90% confidence interval of the true proportion of men who applied to the nursing program.

Answer key is found on page 86.

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