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Kim wants to determine a 90% confidence interval for the true mean birth weight of full...

Kim wants to determine a 90% confidence interval for the true mean birth weight of full term babies. How large of a sample must she have to get a margin of error less than 4 ounces? Assume the population standard deviation is 7 ounces.

Math   Statistics-And-Probability   
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Answer #1

Solution :

Given that,

standard deviation = = 7

margin of error = E = 4

At 90% confidence level the z is ,

= 1 - 90% = 1 - 0.90 = 0.10

/ 2 = 0.10 / 2 = 0.05

Z/2 = Z0.05 = 1.645

Sample size = n = ((Z/2 * ) / E)2

= ((1.645 * 7) / 4)2

= 8.28 = 9

Sample size = 9

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