SOLUTION: Last year, a study showed that the average ATM cash withdrawal took 65 seconds with a standard deviation of 10 seconds. The study is to be repeated this year. How large a sample wo

Question 154857This question is from textbook
: Last year, a study showed that the average ATM cash withdrawal took 65 seconds with a standard deviation of 10 seconds. The study is to be repeated this year. How large a sample would be needed to estimate this year's mean with 95 percent confidence and an error of �4 seconds? This question is from textbook

Answer by Fombitz(32388) (Show Source): You can put this solution on YOUR website!
Assuming a normal distribution and using the old standard deviation as a measure of the standard deviation,
you can use the confidence interval formula,

For 95% confidence, z=1.96.

To be sure, we'll round up to N=25.

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