document.write( "Question 154857This question is from textbook
\n" ); document.write( ": 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? \n" ); document.write( "
Algebra.Com's Answer #114024 by Fombitz(32388)\"\" \"About 
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Assuming a normal distribution and using the old standard deviation as a measure of the standard deviation,
\n" ); document.write( "you can use the confidence interval formula,
\n" ); document.write( "\"z%2Asigma%2Fsqrt%28N%29=4\"
\n" ); document.write( "For 95% confidence, z=1.96.
\n" ); document.write( "\"1.96%2A10%2Fsqrt%28N%29=4\"
\n" ); document.write( "\"sqrt%28N%29=1.96%2A10%2F4\"
\n" ); document.write( "\"N=%2819.6%2F4%29%5E2\"
\n" ); document.write( "\"N=24.01\"
\n" ); document.write( "To be sure, we'll round up to N=25.
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