Recession effect on counts: Sahara, Tata, Singhania, and Birla each had 250 industries last year. This year each sold 10 factories. What is their average number of industries now?

Introduction / Context:
When each member of a set changes by the same amount, the average changes by that same amount. Here, a uniform decrease occurs for all four companies.

Given Data / Assumptions:

• Four companies, each had 250 industries last year.
• Each sold 10 factories this year.

Concept / Approach:
If every element decreases by 10, the average also decreases by 10. So new average = old average - 10.

Step-by-Step Solution:

Verification / Alternative check:
Totals: old total = 4*250 = 1000; new total = 4*(250 - 10) = 4*240 = 960; average = 960/4 = 240.

Why Other Options Are Wrong:

• 260: Would require an increase, not a decrease.
• 25: Unit error (should be industries, not tens).
• None of these: Incorrect since 240 is attainable and correct.

Common Pitfalls:
Forgetting the property that uniform shifts translate directly to average shifts.

Final Answer: