What was the average money with the class of 50 students whose roll numbers are from 1 to 50?

(1) The average money with the first 25 students of the class is $25 more than the average money with the last 25 students.

Let the AVERAGE with last 25 be x, so Average of first 25 is x+25..

Overall average=(x+x+25)/2

But x can be anything..

Insufficient

(2) The average money with the first 25 students is twice the average money with the last 25 students

Let the AVERAGE with last 25 be x, so Average of first 25 is 2x..

Overall average=(x+2x)/2=3x/2

But x can be anything..

Insufficient

Combined...

3x/2=(2x+25)/2........6x=4x+50....x=25

Overall average=75/2

Suff

C

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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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