Question

the average weight of randomly selected 28 adult males was 65kigs. with standard deviation of 2.2 kgs. find a 99% confidence interval

Answer 1

The formula to calculate a confidence interval for a population mean is as follows:

$CI=\bar{x}\pm z\cdot\cfrac{s}{\sqrt{n}},$

where:

• $\bar{x}=65$ : sample mean
• z: the chosen z-value, for a 99% confidence interval z = 2.576
• $s=2.2$ :  sample standard deviation
• n = 28:  sample size.

So,

$CI=65 \pm 2.576\cdot\cfrac{2.2}{\sqrt{28}}=\\= 65\pm1.07=(63.93, 66.07).$