talaangoshtari wrote:There are at least three times as many boys as girls in a class. On a test, the boy's average score is 78, and the girl's average score is 94. Which of the following could be the average test score for the entire class?
Indicate all such valies.
A.88
B.86
C.84
D.82
E.80
The prompt implies that more than one of the five answer choices might be correct.
On the GMAT, only ONE of the five answer choices will be correct.
What is the source of this problem?
Let B = the number of boys, G = the number of girls, and A = the average for the entire class.
There are at least three times as many boys as girls in a class.
Test the THRESHOLD:
The smallest possible ratio for boys to girls.
Here, the SMALLEST POSSIBLE RATIO for boys to girls is 3 to 1.
Let B=3 and G=1.
Since the average for the boys is 78 and the average for the girls is 94, we get:
A = (3*78 + 94)/4 = 82.
Since the boys' average is lower than the girls' average, increasing the ratio of boys to girls will LOWER the average for the entire class.
Since the smallest possible ratio of boys to girls yields an average of 82 for the entire class, and increasing the ratio of boys to girls will lower the average for the entire class, the value of A must be 82 or less.
Thus, options
D and E are possible.
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