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Averages

by cypherskull » Sun May 13, 2012 10:16 am
The avg test score on the final exam for students of class period A was 86. On the same exam, the avg test score for students in class period B was 74. Were there more students in class period A than in B?

a) The no. of students in class period A that scored an 86 on the finals was the same as the no. of students in class period B who scored 74 on the final exam.

b) The avg score for all the students in class periods A & B was 81.
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by GMATGuruNY » Sun May 13, 2012 4:46 pm
cypherskull wrote:The avg test score on the final exam for students of class period A was 86. On the same exam, the avg test score for students in class period B was 74. Were there more students in class period A than in B?

a) The no. of students in class period A that scored an 86 on the finals was the same as the no. of students in class period B who scored 74 on the final exam.

b) The avg score for all the students in class periods A & B was 81.
Statement 1: The no. of students in class period A that scored an 86 on the final was the same as the no. of students in class period B who scored 74 on the final exam.
No information about the other students in each class.
INSUFFICIENT.

Statement 2: The avg score for all the students in class periods A & B was 81.
When the classes are combined, the average (81) is closer to the average in class A (86) than to the average in class B (74).
Thus, the number of students in class A must be greater than the number of students in class B: if there are more values yielding an average of 86 than there are values yielding an average of 74, the average when the classes are combined will be closer to 86 than to 74.
SUFFICIENT.

The correct answer is B.
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by bighnarajeast » Mon May 14, 2012 1:55 am
Can you please describe brefely that why you say -- "When the classes are combined, the average (81) is closer to the average in class A (86) than to the average in class B (74).Thus, the number of students in class A must be greater than the number of students in class B".

What's the rule behind this ?
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