You want to obtain a sample to estimate a population mean. Based on previous evidence, you believe the population standard deviation is approximately σ=75.4σ=75.4. You would like to be 95% confident that your estimate is within 5 of the true population mean. How large of a sample size is required? n=____
Solution
standard deviation = =75.4
Margin of error = E = 5
At 95% confidence level the z is ,
= 1 - 95% = 1 - 0.95 = 0.05
/ 2 = 0.05 / 2 = 0.025
Z/2 = Z0.025 = 1.96
sample size = n = [Z/2* / E] 2
n = ( 1.96* 75.4 / 5 )2
n =873.60
Sample size = n =874 rounded
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