DS: directors managers: GMATprep

Agree, the answer is C.

You can also assume that total employees = 100

and p is the percent of directors. then 1-p is the percent of managers.

# of directors = 100*p = 100p
# of managers = 100*(1-p)

Let the average salary of managers be a
let the average salary of directors be b.

Total salary of all employees = salary of managers + salary of directors

= (100 * p * b) + (100 * (1-p) * a)

The average salary of all employees = total salary/100

= (100 * p * b) + (100 * (1-p) * a)/100 = pb + (1-p)a

from 1, a + 5000 = pb + (1-p)a

from 2, b-15000 = pb + (1-p) a

1-2 gives, a+5000-b+15000=0 or a-b = -20000 or b-a = 20000

From 2, b-15000 = pb + a -pa = p(b-a) + a

or b-a-p(b-a) = 15000

or (b-a) (1-p) = 15000

substituting b-a = 20000, you get 1-p = 15000/20000 = 3/4

or p = 1/4

-mathguru