Question

I am interested in doing a survey. I want to know the average GPA of WVU students within .1. I want to be 95% certain. I know the variance of GPAs is .09. How many students do I need to survey?

A. 25

B. 30

C. 35

D. 40

Answer 1

Solution

2  =0.09

standard deviation =   =0.03

Margin of error = E = 0.1

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z/2 = Z0.025 = 1.96

sample size = n = [Z/2* / E] 2

n = ( 1.96*0.3 / 0.1 )2

n =35

Sample size = n =35