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Homework answers / question archive / How large a sample should be selected to provide a 95% confidence interval with a margin of error of 9? Assume that the population standard deviation is 30
How large a sample should be selected to provide a 95% confidence interval with a margin of error of 9? Assume that the population standard deviation is 30. Round your answer to next whole number.
Given that,
Standard deviation = σ = 30
Margin of error = E = 9
At 95% confidence level the z is ,
α = 1 - 95% = 1 - 0.95 = 0.05
α/ 2 = 0.05 / 2 = 0.025
Zα/2 = Z0.025 = 1.96
Sample Size = n = [Zα/2* σ / E] 2
n = ( 1.96* 30 / 9 )2
n = 42.68 or 43
So, Sample Size is 43.
