Question

A doctor at a local hospital is interested in estimating the birth weight of infants. How large a sample must she select if she desires to be 90% confident that her estimate is within 4 ounces of the true mean? Assume that s = 7 ounces based on earlier studies.

Group of answer choices

2

8

3

9

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 * S ) / E)2

= ((1.645 * 7 ) / 4 )2

= 8

Sample size = 8

Option 8 is correct.