Average and Proportion

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Average and Proportion

by deepakb » Tue Oct 05, 2010 8:12 am
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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by GMATGuruNY » Tue Oct 05, 2010 8:54 am
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 A = 4 students. 4*65 = 260 total.
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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by deepakb » Wed Oct 06, 2010 1:56 am
Ohhhhhh.... i was dumb on that.
thanks.

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by Yanat » Wed Oct 06, 2010 7:14 am
In my view it is 75. So I go for B.