Profit and Loss – Two close profit rates reveal the cost price: A person sold a watch at a 10% profit. If he had sold it for ₹ 2000 more, the profit would have been 20%. What is the cost price of the watch?

Introduction / Context:
A fixed-amount increase in selling price moves the profit rate from 10% to 20%. Since both percentages refer to the same cost price, this gives a direct linear equation that can be solved quickly.

Given Data / Assumptions:

• Actual profit rate = 10%
• If SP increased by ₹ 2000 ⇒ profit rate = 20%

Concept / Approach:
Let CP = x. Then SP at 10% is 1.10x. New SP for 20% would be 1.20x, which is ₹ 2000 more than 1.10x. Use this to find x.

Step-by-Step Solution:
1.10x + 2000 = 1.20x2000 = 0.10x ⇒ x = ₹ 20,000

Verification / Alternative check:
At CP ₹ 20,000: 10% SP = ₹ 22,000; 20% SP = ₹ 24,000; difference = ₹ 2000, confirming the condition.

Why Other Options Are Wrong:
₹ 15,000, ₹ 10,000, ₹ 18,000, and ₹ 25,000 do not satisfy the exact ₹ 2000 gap between the two percentage-based SPs.

Common Pitfalls:
Taking 10% and 20% of the selling price instead of cost price; the base is CP.

Final Answer:
₹ 20,000