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Percent of employees as directors!!

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Percent of employees as directors!!

by abhijeet_g » Fri May 10, 2013 11:59 pm
Hi,

Following is the DS ques from GMATPrep.

Each employee on a certain task force is either a manager or a director. What percent of the employees on the task force
are directors?
(1) The average (arithmetic mean) salary of the managers on the task force is $5,000 less than the average salary of all
employees on the task force.
(2) The average (arithmetic mean) salary of the directors on the task force is $15,000 greater than the average salary of all
employees on the task force.

Could anyone help me with this question? Will provide OA after explanations. Thanks.
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by GMATGuruNY » Sat May 11, 2013 12:57 pm
abhijeet_g wrote: Each employee on a certain task force is either a manager or a director. What percent of the employees on the task force
are directors?

(1) The average (arithmetic mean) salary of the managers on the task force is $5,000 less than the average salary of all
employees on the task force.
(2) The average (arithmetic mean) salary of the directors on the task force is $15,000 greater than the average salary of all
employees on the task force.
Clearly, neither statement on its own is sufficient.
The two statements combined constitute a MIXTURE problem: two ingredients (managers and directors) are combined to form a mixture (all of the employees on the task force).
To evaluate the two statements combined, use ALLIGATION -- a great way to handle mixture problems.

Let M = managers, D = directors, and T = the entire task force.

Step 1: Draw a number line, with the two ingredients (M and D) on the ends and the mixture (T) in the middle:
M---------------T---------------D

Step 2: Calculate the distances between the averages.
Since the managers' average is 5000 less than the average of the entire task force, and the directors' average is 15,000 more than the average of the entire task force, we get the following distances between the averages:
M-----5000------T----15000------D

Step 3: Determine the ratio in the mixture.
The ratio of M to D in the mixture is the RECIPROCAL of the distances in red.
M : D = 15000:5000 = 3:1.

Since M : D = 3:1, there are 3 managers for every 1 director.
Thus, of every 4 employees, 1 is a director, implying that directors/total = 1/4 = 25%.
SUFFICIENT.

The correct answer is C.

For two other problems solved with alligation, check here:

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by abhijeet_g » Sat May 11, 2013 7:42 pm
Thanks Mitch....OA is indeed C but I was not able to get it...Many thanks for the above approach guided by you. I have saved this approach of yours. I have my GMAT scheduled coming week..Hoping to apply many of your innovative approaches on this forum. :-)
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