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 = 77.2 σ = 77.2 dollars. You would like to be 90% confident that your estimate is within 5 dollar(s) of average spending on the birthday parties.

How many parents do you have to sample?

Answer #1

Solution :

Given that,

standard deviation = =77.2

Margin of error = E = 5

At 90% confidence level

= 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 *77.2 /5 )2

n =645.099

Sample size = n =645

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