A researcher wants to find an 80% confidence interval for the mean commute time for CBC students.

Question

From similar studies at other community colleges, the researcher estimates the standard deviation of the study will be around s = 17.5 minutes. If they want the maximum error to be 4 minutes, find the minimum sample size needed for the study.

Answer 1

When your given the std. dev.(1.75) & the margin of error(4), the formula in order to determine the sample size is, 

n= ((z * σ)/MOE)².

In this formula, z is the z value obtained from the Z distribution table. σ is the population standard deviation of the data set (1.75 in this case). The MOE is the margin of error that is desired(4 in this case).

Plug in those numbers in this equation sill give you the answer.