Price tweak thought experiment — same gain% after buying cheaper and selling cheaper A dealer sells a radio at a 10% gain. If instead he had bought it 10% cheaper and also sold it for Rs 132 less, he would still have a 10% gain. What is the radio's original cost price?

Introduction / Context:
This is a consistency check under an alternative plan: a 10% cheaper purchase and Rs 132 lower selling price still yield 10% profit. Comparing the two expressions for the alternate selling price reveals the original cost.

Given Data / Assumptions:

• Original CP = x; original SP = 1.10x.
• Alternate CP' = 0.90x.
• Alternate SP' = (original SP − 132) and must equal 1.10 × CP' = 1.10 × 0.90x = 0.99x.

Concept / Approach:
Set (1.10x − 132) = 0.99x and solve for x.

Step-by-Step Solution:
1.10x − 132 = 0.99x.(1.10 − 0.99)x = 132 ⇒ 0.11x = 132 ⇒ x = 132/0.11 = 1,200.

Verification / Alternative check:
Original: CP 1,200 ⇒ SP 1,320. Alternate: CP' 1,080; SP' must be 1.10 × 1,080 = 1,188, and indeed 1,320 − 132 = 1,188.

Why Other Options Are Wrong:
1,188 is the alternate SP, not CP; 1,320 is the original SP; others don't satisfy the equality.

Common Pitfalls:
Confusing SP with CP or failing to apply the 10% to the correct base in each plan.

Final Answer:
Rs 1,200