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please help

by sana.noor » Sat Jun 08, 2013 1:44 am
Of all the players in a professonal baseball league, 1/2 are foreign-born,inclding 1/3 of the pitchers. If 3/4 of the players are pitchers, what percentage of the players who are not pitchers are foreign-born?

A) 100%
B) 75%
C) 66 2/3%
D) 50%
E) 25%

OA is A
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by GMATGuruNY » Sat Jun 08, 2013 2:23 am
sana.noor wrote:Of all the players in a professonal baseball league, 1/2 are foreign-born,inclding 1/3 of the pitchers. If 3/4 of the players are pitchers, what percentage of the players who are not pitchers are foreign-born?

A) 100%
B) 75%
C) 66 2/3%
D) 50%
E) 25%

OA is A
This is an EITHER/OR problem.
Every player is EITHER a pitcher OR a non-pitcher.
Every player is EITHER foreign-born OR not.
Use a GROUP GRID (also known as a matrix) to organize the data:

_______________P__________NP___________Total

F:

NF:

Total:


In the group grid, every row has to add up to the total, as does every column.
Looking at the top row, foreign-born pitchers + foreign-born non-pitchers = total foreign born.
Looking at the left-most column, foreign-born pitchers + non-foreign-born pitchers = total pitchers.

Now let's fill in the data step by step. Whenever we have 2 entries in a row or column, we can determine the remaining entry, since everything has to add up horizontally and vertically. For the total number of players, let's plug in 12 (the LCM of 2, 3 and 4, the denominators in the problem):

_______________P__________NP____________Total

F:

NF:

Total:_____________________________________12




1/2 are foreign-born, 3/4 are pitchers:

________________P__________NP____________Total

F:__________________________________________6

NF:_________________________________________6

Total:____________9__________3______________12




1/3 of the 9 pitchers are foreign-born:

_________________P__________NP___________Total

F:_______________3___________3______________6

NF:______________6___________0______________6

Total:____________9___________3_____________12




Notice that everything adds up horizontally and vertically.

Foreign-born NP/Total NP = 3/3 = 100%.

The correct answer is A.
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by Brent@GMATPrepNow » Sat Jun 08, 2013 5:00 am
I thought I'd point out that Mitch's "group grid" approach is also known as the Double Matrix Method. This technique 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 baseball players, and the two characteristics are:
- foreign-born or not foreign-born
- pitcher or non pitcher

To learn more about this technique, 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

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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