Question

A researcher is interested in determining the average number of years new teachers remain in the classroom. If past information shows a standard deviation of 5 years, what size sample should be taken so that at 95% confidence the margin of error will be 6 months or less?

Answer 1

Answer: 385

Given: error: 6 months, standard deviation = 5 years is 60 months

Step 1: find the minimal sample size ‘n’ for 95% confidence interval

1-0.95= 0.05

0.05/2= 0.025

Step 2:
1-0.025= 0.975

View attachment for more steps