SOLUTION: 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 approximate

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Question 1197458: 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=30.4 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 moms do you have to sample? Do not round mid-calculation.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!

Hi  
 90% confident  ⇒  z = 1.645
σ = 30.4,   ME = 5
How large of a sample size is required?
ME+=+z%2Asigma%2Fsqrt%28n%29
0r
n = %28+z%2Asigma%2FME%29%5E2
n = %28%281.645%2A30.4%29%2F5%29%5E2+%29%29 = 100.0320  0r sample Size =101 (always round Up)

 = CI	z = value
90%	z =1.645    Invnorm(.95)  2-sided (.90 + .10/2 = .95 )
92%	z = 1.751
95%	z = 1.96
98%	z = 2.326  
99%	z = 2.576
Wish You the Best in your Studies.