# Sample Size

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Question: Hockey-r-us" a store specializing in sales of hockey equipment, wants to find out the average age of all it's customers. A random sample 25 customers reveals an average age of 38 years, with a standard deviation of six years.

How large of a sample should be constructed to be 90% confident that the sampling error is one or less?

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##### Solution Summary

Calculates the sample size for a given level of sampling error.

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Mean=M 38 years

Standard deviation =s= 6 years

(sample mean-M )= 1 (to ensure estimate is within 1 of M )

sx=standard error of mean=s/square root of n

z value corresponding to 90% confidence= 1.6449

z=(sample mean-M )/sx= 1.6449 ...

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