canbtg wrote:Each of people voted once in an election, X got 483 from male voters, Y got 433 from female voters. How many votes did X get?

1) X got votes from 50% of male voters
2) Y got votes from 60% of female voters

We can use the Double Matrix Method here to help us arrange our information. The Double Matrix can be used for most questions featuring a population in which each member has two characteristics associated with it.
Here, we have a population of voters, and the two characteristics are:
- male or female
- voted for X or voted for Y

So, we can set up out diagram as follows:


X got 483 from male voters, Y got 433 from female voters.
We can add that information as follows:


Target question: How many votes did X get?
Notice that the two blue boxes represent the males and females who voted for X.

So, our goal here is to find the sum of these two boxes.

Statement 1: X got votes from 50% of male voters
The two highlighted boxes represent the male voters. If 50% of them voted for X, then the other 50% voted for Y.



So, 483 of the males also voted for Y...


We can now see that we don't have enough information to find the sum of the values in the 2 blue boxes


As such, statement 1 is NOT SUFFICIENT


Statement 2: Y got votes from 60% of female voters
The two highlighted boxes represent the female voters.

Let's let F = the total number of female voters.
If 60% of the females voted for Y, then we can write 0.6F = 433
If we wanted to, we COULD solve this equation for F, at which point we COULD ALSO determine the number of females who voted for X.
Since we COULD determine the number of females who voted for X, then we COULD ALSO find the total number of people who voted for X

Since we could easily answer the target question with certainty, statement 2 is SUFFICIENT

Answer: B

To learn more about the Double Matrix Method , watch our free video: https://www.gmatprepnow.com/module/gmat- ... ems?id=919

Then try these additional practice questions that can be solved using the Double Matrix Method:
- https://www.beatthegmat.com/mba/2011/05/ ... question-1
- https://www.beatthegmat.com/mba/2011/05/ ... question-2
- https://www.beatthegmat.com/mba/2011/05/ ... question-3
- https://www.beatthegmat.com/ds-quest-t187706.html
- https://www.beatthegmat.com/overlapping- ... 83320.html
- https://www.beatthegmat.com/finance-majo ... 67425.html
- https://www.beatthegmat.com/ds-french-ja ... 22297.html
- https://www.beatthegmat.com/sets-t269449.html#692540
- https://www.beatthegmat.com/in-costume-f ... tml#692116

Cheers,
Brent

canbtg wrote:thanks Brent . The question is from GMATPREP QP .

Hmmm, if it's an official GMATPrep question then either I'm missing something totally basic, or the question was not transcribed correctly. Here's why:

Let's let F = the total number of female voters.
It is given that 433 of the females voted for Y
Statement 2 say that 60% of the females voted for Y.
This mean that we can write 0.6F = 433
So, F = 433/0.6 = 721 2/3
This doesn't make any sense. We can't have 721 2/3 females.

Cheers,
Brent

Good work.
483 works much better.

Cheers,
Brent