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Good GMATprep sum

by rb90 » Mon Sep 27, 2010 4:45 am
Image

The square shows the correct answer. Can someone please help me out in how to go about this sum?
Thanks.
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Source: — Data Sufficiency |
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by Jim@Grockit » Mon Sep 27, 2010 7:06 am
rb90 wrote:Image

The square shows the correct answer. Can someone please help me out in how to go about this sum?
Thanks.
To get the ratio we need the actual number of both males and females, or the ratio itself.

Statement (1) gives us the number of males but nothing else. INSUFFICIENT
Statement (2) gives us the complete basis for a weighted average equation (and is therefore SUFFICIENT):

([number of males * 9.8] + [number of females * 9.1]) / [number of males + number of females] = 9.3

same equation rewritten: (9.8m + 9.1n)/m+n = 9.3

If you had to do the math (which you don't, it's Data Sufficiency), then:
9.8m + 9.1n = 9.3m + 9.3n
.5m = .2n
m/n = 2/5
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