The grades on the final examination given in a large organic chemistry class are

Question

The grades on the final examination given in a large organic chemistry class are normally distributed with a mean of 72 and a standard deviation of 8. The instructor of this class wants to assign an “A” grade to the top 10% of the scores, a “B” grade to the next 10% of the scores, a “C” grade to the next 10% of the scores, a “D” grade to the next 10% of the scores, and an “F” grade to all scores below the 60th percentile of this distribution. For a letter grade of A, find the lowest acceptable score within the established range. Provide your answer in the format XX.X, for example, 93.4.

Explanation / Answer

From standard normal tables we get:

P(Z > 1.282 ) = 0.1

Therefore the z score for the minimum score required to get an A would be given as: 1.282

Now the required score is thus computed as:

= Mean + 1.282*Std Dev

= 72 + 1.282*8

= 82.256

Therefore 82.3 is the required score here.

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