Question

How large a sample should be taken to be 95% sure that the error of estimation does not exceed

0.2 unit when standard deviation is 5?

Answer 1

define the sample size n = ( (z * standard deviation) / (margin of error ) )²

z at 95% confidence from the normal table is 1.96

Thus substituting in the above, we obtain

sample size = ( 1.96 * 5 / 0.2 )²

= (49)²

= 2401