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
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average score
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Lets assume there are 4x students in first class
6x in second class and 5x in the third class
Avg of 1st class = 65 => Total of 1st class = 65*4x ---(1)
Avg of 2nd class = 80 => Total of 2nd class = 80*6x ---(2)
Avg of 3rd class = 77 => Total of 3rd class = 77*5x ---(3)
Total no of students (all classes combined) = 4x+6x+5x = 15x ----(4)
Avg score for the combined class [(1) + (2) + (3)]/(4) = 75
OA??
6x in second class and 5x in the third class
Avg of 1st class = 65 => Total of 1st class = 65*4x ---(1)
Avg of 2nd class = 80 => Total of 2nd class = 80*6x ---(2)
Avg of 3rd class = 77 => Total of 3rd class = 77*5x ---(3)
Total no of students (all classes combined) = 4x+6x+5x = 15x ----(4)
Avg score for the combined class [(1) + (2) + (3)]/(4) = 75
OA??
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AleksandrM
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