IMO C

1 is clearly insufficient because we have no information regarding directors here..
2 is clearly insufficient because we have no information regarding managers here..

lets take both together..

say,
d = number of directors.
m = number of managers.
D is the average salary of directors.
M is the average salary of managers.
S is the total average salary.

M = S - 5000 (from 1) .... (1)
D = S + 15000 (from 2) .... (2)

Total salary = (d+m)S .. total number of task force members (m + d) times the total average salary
Total salary = mM + dD .. total salary of Managers + total salary of Directors

(d+m)S = mM + dD .. (I)

(1).m ==>
mM = mS - m5000 ..(3)
(2).d ==>
dD = dS + d15000 ..(4)

(3) + (4) ==>
mM + dD = (m+d)S + d15000 - m5000 .. (II)


I and II ==>

d15000 - m5000 = 0

d/m = 1/3

d/d+m = 1/4

So both of them together are sufficient. Thus C.

d=# of directors and m=# of managers. Total = d+m. sal(x) represents avg salary of x people.
a) sal(m) = sal(d+m)-5000 insufficient.
b) sal(d) = sal(d+m)+15000 insufficient.
a&b together)
total salary = total salary of managers + total salary of directors
sal(m+d)*(m+d) = sal(m)*m + sal(d)*d
sal(m+d)*(m+d) = m*sal(d+m)-5000m + d*sal(d+m) + 15000d
=> 5000m=15000d =>m=3d
%of directors = d/(d+m) = d/(d+3d) = 1/4
IMO C

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 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 salary of the directors on the task force is 15,000 greater than the average salary of all employees on the task force.

Each statement is clearly insufficient on its own.

When combining the statements, we can plug in for the average salary of all the employees and use alligation.

Let:
A = average salary of all the employees.
M = average salary of the managers.
D = average salary of the directors.

Let A = 10,000.
M = 10,000 - 5000 = 5000.
D = 10,000 + 15,000 = 25,000.

This is a weighted average question: What ratio of managers (with an average salary of 5000) to directors (with an average salary of 25,000) will yield a company with an average salary of 10,000?

We can use alligation to determine the ratio:

The proportion needed of each element in the mixture is the positive difference between the average attributed to the other element and the average attributed to the final mixture.

Proportion needed of M = 25,000-10,000 = 15,000.
Proportion needed of D = 10,000-5,000 = 5000.
M : D = 15,000 : 5000 = 3:1.
Since 3+1=4, D = 1/4 = 25%.

The correct answer is C.