Price adjustment scenario — A shopkeeper sells a transistor at 15% above its cost. If instead he had bought it at 5% more than his original cost and also sold it for ₹ 6 more than his original selling price, he would have made 10% profit. What is the (original) cost price of the transistor?

Introduction / Context:
This is a two-scenario price puzzle. In the real scenario, the seller gains 15% over cost. In a hypothetical scenario, both the cost and selling price are adjusted, resulting in a 10% profit. We form an equation in the unknown cost price and solve.

Given Data / Assumptions:

• Let original cost = C; original selling price = 1.15C.
• Alternate scenario: new cost = 1.05C; new selling price = 1.15C + ₹ 6.
• Alternate profit = 10% ⇒ new SP = 1.10 * new cost.

Concept / Approach:
Set 1.15C + 6 = 1.10 * (1.05C) and solve for C. This linear equation gives the original cost price directly.

Step-by-Step Solution:

Verification / Alternative check:
Original SP = 1.15 * 1200 = ₹ 1380. Alternate: cost = 1260; SP = 1386 ⇒ profit = 126 ⇒ 10% of 1260, consistent.

Why Other Options Are Wrong:
₹ 800, ₹ 900, ₹ 1000, and ₹ 1400 do not satisfy the equation 1.15C + 6 = 1.155C.

Common Pitfalls:
Adding or subtracting the percentages instead of multiplying, or forgetting that the alternate 10% is on the new cost.

Final Answer:
₹ 1200