Question

A sample of 81 was taken from a population with a standard deviation of 45 kilograms. If the sample mean was 112 kilograms, the mean of any other sample of 81 will be within what range 99.7% of the time?

A. 97 kilograms to 127 kilograms
B. 102 kilograms to 122 kilograms
C. 92 kilograms to 132 kilograms
D. 107 kilograms to 117 kilograms

Answer 1

Sample size = n = 81
Population Standard Deviation = s = 45
Sample Mean = x = 112

Since, population standard deviation is known, we will use z distribution to find the confidence interval.

The critical z value for 99.7% is 2.968

So, the confidence interval will be:

$(112-2.968* \frac{45}{ \sqrt{81} }, 112-2.968* \frac{45}{ \sqrt{81} }) \\ \\ (97.16, 126.84)$

Rounding of to nearest integers the confidence interval will be 97 to 127.

So, option A gives the correct answer