Staff salary mix problem (officers vs non-officers): The average daily salary of the entire staff is ₹200. Officers average ₹550 per day and non-officers average ₹120 per day. If there are 16 officers, how many non-officers are there?

Introduction / Context:
This is a classic mixture (weighted average) problem involving two subgroups with different averages contributing to an overall average.

Given Data / Assumptions:

• Total average = ₹200
• Officer average = ₹550; Non-officer average = ₹120
• Number of officers = 16; number of non-officers = n

Concept / Approach:
Overall average = (sum of subgroup totals)/(total people). Set up equation with n unknown and solve.

Step-by-Step Solution:
(16 * 550 + n * 120) / (16 + n) = 2008800 + 120n = 200 * (16 + n)8800 + 120n = 3200 + 200n8800 - 3200 = 200n - 120n5600 = 80n → n = 70

Verification / Alternative check:
Plug n = 70 back to confirm overall average = ₹200 exactly.

Why Other Options Are Wrong:
60, 65, 68, 72 do not satisfy the balance of totals implied by the given averages.

Common Pitfalls:
Setting denominator incorrectly or mixing rupee totals with averages; always convert to totals first.

Final Answer:
70