Question

A child psychologist wants to estimate the mean age at which a child learns to talk. Find the sample size necessary for a 90% confidence level to ensure that the sample mean is within 5 weeks for the mean age at which a child learns to talk. Assume standard deviation =10 weeks

Answer 1

Solution :

Given that,

standard deviation =s =   =10

Margin of error = E = 5

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 *10 / 5 )2

n =10.8

Sample size = n =11 rounded