Question

How large a sample should be selected to provide a 95% confidence interval with a margin of error of 4? Assume that the population standard deviation is 30 . Round your answer to next whole number.

Answer #1

Solution :

Given that,

standard deviation = = 30

margin of error = E = 4

At 95% confidence level the z is ,

= 1 - 95% = 1 - 0.95 = 0.05

/ 2 = 0.05 / 2 = 0.025

Z_{/2}
= Z_{0.025} = 1.960

Sample size = n = ((Z_{/2}
*
) / E)^{2}

= ((1.960 * 30) / 4 )^{2}

= 216.09

= 216

Sample size = 216

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Find the margin of error for a 95% confidence interval for
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(i) Find the margin of error for a 95% confidence interval for
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(ii).
(ii) Find the margin of error for a 95% confidence interval
for estimating the population mean when the...

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