Question

A report in a research journal states that the average weight loss of people on a certain drug is lbs with a margin of error of $\pm5$ lbs with confidence level C = 95%.

(a) According to this information, the mean weight loss of people on this drug, $\mu$ , could be as low as________ lbs.

(b) If the study is repeated, how large should the sample size be so that the margin of error would be less than 2.5 lbs? (Assume $\sigma = \ 8$ lbs.)
ANSWER: ______

Answer 1

Solution:

(a) 18 - 5 = 13
as low as 13 lbs.
According to this information, the mean weight loss of people on this drug, \mu , could be as low as 13 lbs.
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(b) Margin of error = 2.5
=> z *σ/√n = 2.5
=> 1.96 * 8/√n = 2.5
=> n = (1.96 * 8/2.5)²
=> n = 40