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=21.9σ=21.9 dollars. You would like to be 95% confident that your estimate is within 3 dollar(s) of average spending on the birthday parties. How many moms do you have to sample

Answer 1

Solution :

Given ,

= 21.9 ..Population SD

E = 3 Margin of error

c = 95% = 0.95 ...confidence level

Find sample size required.

c = 0.95

= 1- c = 1- 0.95 = 0.05

  /2 = 0.025

Using Z table ,

= 1.96

Now, sample size (n) is given by,

=  {(1.96* 21.9 )/ 3 }²

=  204.718864

= 205 ..(round to the next whole number)

Answer : Required Sample size is n = 205