The average salary of the entire staff of an office is Rs $120$ per month. The average salary of officers is Rs $460$ and that of non-officers is Rs $110$. If the number of officers is $15$, the number of non-officers is:

Question

The average salary of the entire staff of an office is Rs $120$ per month. The average salary of officers is Rs $460$ and that of non-officers is Rs $110$. If the number of officers is $15$, the number of non-officers is:

Option A

150

Option B

255

Option C

340

Option D — Correct answer

510

Correct choice.

Explanation

Using weighted averages, the count ratio is based on deviations from the mean. Non-officers $=15\times\frac{460-120}{120-110}=15\times34=510$.

Chapter Mock 6: Average and Ages