The scores for a mathematics course seem to be normally distributed with mean 70 & standard deviation of 8. If the instructor wishes to give an A grade to 10% of the students, what should be the dividing line between an A grade and a B grade?
Let's find the 90th percentile; the closest value in z-table is 0.8997, it corresponds to z = 1.28.
So,
Thus, 80 should be the dividing line between an A grade and a B grade.
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