Question

You want to obtain a sample to estimate how much parents spend on their kids birthday parties. Based on previous study, you believe the population standard deviation is approximately σ=37.8σ=37.8 dollars. You would like to be 90% confident that your estimate is within 10 dollar(s) of average spending on the birthday parties. How many parents do you have to sample?

Answer 1

Solution :

Given that,

standard deviation =   =37.8

Margin of error = E = 10

At 90% confidence level of z is

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05 = 1.645

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

n = ( 1.645 *37.8 /10 )2

n =38.66

Sample size = n =39