Question

A shoe store wants to see the average number of times that customers come to the store during the week. What would be the sample size if they wanted to be 90% sure that the sample mean is within 3.4 and has a standard deviation of 12.6?

Answer 1

Solution :

Given that,

standard deviation =s =   =12.6

Margin of error = E = 3.4

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z 0.05 = 1.645

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

n = ( 1.645 * 12.6 / 3.4 )2

n =37.16

Sample size = n =37