Profit and Loss – Equal profit and loss amounts at two selling prices: The profit when selling a commodity for Rs 425 equals the loss when selling it for Rs 355. What is the cost price of the commodity?

Introduction / Context:
This is a symmetric profit–loss setup: the deviation of the selling price above cost equals the deviation below cost at another selling price.

Given Data / Assumptions:

• SP at profit = Rs 425
• SP at loss = Rs 355
• Profit amount = Loss amount

Concept / Approach:
If CP = x, then 425 - x = x - 355. Solve for x.

Step-by-Step Solution:
425 - x = x - 3552x = 425 + 355 = 780x = 780 / 2 = 390

Verification / Alternative check:
Profit at Rs 425 is 35; loss at Rs 355 is also 35; they match.

Why Other Options Are Wrong:
385, 395, 400, and 380 do not make equal deviations from both selling prices.

Common Pitfalls:
Adding or subtracting incorrectly; forgetting that deviations are symmetric around CP.

Final Answer:
Rs 390