Question

How many women must be randomly selected to estimate the mean weight of women in one age group. We want 90% confidence that the sample mean is within 2.3lb of the population mean, and the population standard deviation is known to be 14 lb.

143

202

126

101

Answer 1

Solution :

Given that,

standard deviation =   =14

Margin of error = E = 2.3

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 * 14 /2.3 )2

n 100.26

Sample size = n =101