A teacher gave the same test to three history classes: A, B, and C. The average

(arithmetic mean) scores for the three classes were 65, 80, and 77, respectively. The ratio

of the numbers of students in each class who took the test was 4 to 6 to 5, respectively.

What was the average score for the three classes combined?

A. 74

B. 75

C. 76

D. 77

E. 78

## Average and Proportion

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Plug in A = 4 students. 4*65 = 260 total.deepakb wrote:A teacher gave the same test to three history classes: A, B, and C. The average

(arithmetic mean) scores for the three classes were 65, 80, and 77, respectively. The ratio

of the numbers of students in each class who took the test was 4 to 6 to 5, respectively.

What was the average score for the three classes combined?

A. 74

B. 75

C. 76

D. 77

E. 78

Plug in B = 6 students. 6*80 = 480 total.

Plug in C = 5 students. 5*77 = 385 total.

Total of all scores = 260+480+385 = 1125.

Total number of students = 4+6+5 = 15.

Average = 1125/15 = 75.

The correct answer is B.

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