Question

4. What is the minimum sample size to select to find the mean number of absences per month for school children, within ±0.2 points at a 95 % Confidence Level if it is known that the standard deviation is 1.1 days?

Answer 1

Solution

standard deviation =s =   =1.1

Margin of error = E = 0.2

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*1.1 / 0.2 )2

n =116.2084

Sample size = n =116