ExplanationIf the class average is 82% on a 50-point test, the average score was 41 points out of 50.

Use the Average Pie to find the sum of the class’s scores: (41)(32) = 1,312. To reach a class average of 86%, each student will need to average 43 points out of 50 points. Use the Average Pie to find the desired sum of the class’s scores: (43)(32) = 1,376. The difference is 1,376 − 1,312 = 64, so the class needs to make up 64 points;\(\frac{64}{4} =16\), so 16 students need to answer the extra credit question correctly.

The answer is B. Alternatively, notice that the class’s average needs to increase by 4%, or 2 points on average for a 50-question test. But the extra credit is

worth 4 points, so to average half of a 4-point increase, only half the students (16) need to get the extra credit correct.

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Sandy

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