6.25 Determining sample size. Refer to the previous exercise. You really want to use a sample size such that about 95% of the averages fall within ±5 minutes of the true mean μ = 6.78.

1. (a) Based on your answer to part (b) in Exercise 6.24, should the sample size be larger or smaller than 175? Explain.

2. (b) What standard deviation of do you need such that 95% of all samples will have a mean within 5 minutes of μ?

3. (c) Using the standard deviation you calculated in part (b), determine the number of students you need to sample.