Question

The company wants to sell t-shirts and owner  wants to be 95% certain of the results, and she wants to be within $1,000 of the true mean. When she was researching online, she found that the standard deviation of the mean t-shirt sales for businesses similar to hers was $2,200.

How many should she get data from?

Answer 1

Solution :

Given that,

standard deviation = =  $\sigma$ =2200

Margin of error = E = 1000

At 95% confidence level the z is ,

$\alpha$ = 1 - 95% = 1 - 0.95 = 0.05

$\alpha$ / 2 = 0.05 / 2 = 0.025

Z_$\alpha$/2 = Z_0.025 = 1.96

sample size = n = [Z_$\alpha$/2* $\sigma$ / E] ²

n = ( 1.96* 2200 / 1000 )²

n =18.59