document.write( "Question 1141128: You want to estimate the mean time college students spend watching online videos each day. The estimate must be within 1 minute of the population mean, and you want to be 99% confident in your estimate. What sample size would be required if the standard deviation of viewing time is 2.4 minutes? \n" ); document.write( "
Algebra.Com's Answer #761855 by Boreal(15235)![]() ![]() You can put this solution on YOUR website! want a t-test but estimate first with a z, since the z (0.995) is the same regardless of the sample size, whereas the t-value changes. \n" ); document.write( "error=t*s/sqrt(n) use 2.576 for z in place of t \n" ); document.write( "1=2.576*2.4/sqrt(n) \n" ); document.write( "square both sides and multiply through by n \n" ); document.write( "n=38.22 or 39 \n" ); document.write( "now try tdf=38,0.995 which is 2.72 \n" ); document.write( "2.72*2.4/sqrt(39)=1.04, too big. \n" ); document.write( "and with a few iterations, a sample size of 42 will be found to give an error of 0.9998, under 1. \n" ); document.write( " |