Normal Distribution with Regards to Time and Percentages

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The length of time for students to complete a test is found to be normally distributed with mean 70 minutes and standard deviation 12 minutes. How long should the time for the test be if we wish for 90 percent of the students to complete the test in less time than the test length? (Use the Normal table provided for your calculations)

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Hint: look in the normal table to find how many standard deviations you need to be above the mean to have $90\%$ of the area to the left.

How does the $-6\sigma $ student finish in $-2$ minutes?