document.write( "Question 1203211: A sample of 40 sales receipts from a grocery store has x= 137 and s=30.Use these values to test whether or not the mean is sales at the grocery store are different from 150. \n" ); document.write( "
Algebra.Com's Answer #838592 by Theo(13342)\"\" \"About 
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sample size = 40
\n" ); document.write( "sample standard deviation = 30
\n" ); document.write( "sample mean = 137
\n" ); document.write( "test mean = 150
\n" ); document.write( "standard error of test is standard deviation / square root of sample size = 30 / sqrt(40) = 4.7434.
\n" ); document.write( "since sample standard deviation is used, rather than population standard deviation, use of t-score is indicated.
\n" ); document.write( "t = (x - m) / s
\n" ); document.write( "t is the t-score
\n" ); document.write( "x is the sample mean
\n" ); document.write( "m is the test mean
\n" ); document.write( "s is the standard error.
\n" ); document.write( "formula becomes t = (137 - 150) / 4.7434 = -2.74065.
\n" ); document.write( "area to the left of that t-score with 39 degrees of freedom = .00436017756.
\n" ); document.write( "that's your test alpha.
\n" ); document.write( "two tailed critical alpha on the low side of the confidence is typically as low as .005.
\n" ); document.write( "test alpha is less than that, so results are significant, indicating the sales at the grocery store are diffeenct from the test sales mean of 150.
\n" ); document.write( "note that .005 critical alpha is very restrictive.
\n" ); document.write( "it is normally .025 (that's .95 confidence interval with two tailes totaling .05, with .025 on each end.\r
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