gmat prep question

[jerseygirl]

please help.
C
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[limestone]

I have a long approach, hope it can help.

Let the proportion of managers be "x", that of directors be "y", then x + y = 1 ( or 100%)
Let the average salary of managers be "a", that of directors be "b" then the average salary of all employees :
(ax + by)/ (x+y) = ax + by ( as x + y = 1)

(1) a - (ax + by) = -5000
There're four unknows here, and there's only one relation between x & y ( x + y = 1) => insuff

(2) alone: b - (ax +by) = 15000; like (1) => insuff

(1) & (2)
take (2) - (1) = b- (ax + by) - a + (ax + by) = 15000 + 5000
or b - a = 20000 or b = a + 20000

Now replace b with a + 20000 into (1): a - ( ax + (a+20000)y) = a - ( ax + ay + 20000y) = a - ( a*(x+y) + 20000y) = a - a - 20000y = -20000y = -5000
or y = -5000/-20000 = 0.25
then x = 1 - 0.25 = 0.75
So the percent of employees in the task force is directors is 25%, managers is 75% => suff
C is the answer.

[neerajkumar1_1]

question has already been discussed..

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