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Question: Weights of women in one age group are normally distributed with a standard deviation σ of 18 lb. A researcher wishes to estimate the mean weight of all women in this age group. Find how large a sample must be drawn in order to be 90 percent confident that the sample mean will not differ from the population mean by more than 3.8 lb.

Pick the Right Answer:

a. 61

b. 87

c. 62

d. 59

Answer: z=(x bar- mu)/(sigma/sqrt(n))
or, 1.65=(3.8)/(18/sqrt(n)) [sample mean - popon mean=3.8]
or, n=(18*1.65/3.8)^2=61(Ans.)  Edit

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