Question

How many women must be randomly selected to estimate the mean weight of women in one age group. We want 90% confidence that the sample mean is within 3.7 lb of the population mean, and the population standard deviation is known to be 28 lb.

Answer 1

Answer: the required sample size = 155

Explanation:

If the standard deviation of the prior study is known, then the formula to compute required sample size:

`n=((z^**\sigma)/(E))^2`, where E = Margin of error, z* = Critical value,
`\sigma` = populion standard deviation.

Given: E = 3.7 ,
`\sigma=28`

Critical value for 90% confidence = 1.645

Required sample size:
`n=((1.645*28)/(3.7))^2`

`n=(12.4486486486)^2\approx155`

Hence, the required sample size = 155