document.write( "Question 1160672: The times a teacher takes to grade one page of an exam are normally distributed with a mean of 4 minutes and a standard deviation of 1 minute. For about what percent of exams does a teacher grade one page in less than 7 minutes?
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Algebra.Com's Answer #852044 by greenestamps(13200) $\"\"$ $\"About$

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\n" ); document.write( "Here is a different method than shown by the other tutor for doing the calculations.

\n" ); document.write( "The basic rule is that 99.7% of scores in a normal distribution are within 3 standard deviations of the mean. That means 0.3% of the scores are more than 3 standard deviations from the mean.

\n" ); document.write( "That 0.3% is equally split between the scores that are more than 3 standard deviations above the mean and the ones that are more than 3 standard deviations below the mean, so 0.15% of the scores are more than 3 standard deviations above the mean.

\n" ); document.write( "And that means that the percentage of scores that are less than 3 standard deviations above the mean is 100 - 0.15 = 99.85.

\n" ); document.write( "ANSWER: 99.85%

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