The marked price of an article is increased by 25% and the selling price is increased by 16.66%. As a result, the profit doubles. If the original marked price is Rs 400 and exceeds cost by 33.33%, find the increased selling price.

Introduction:
This problem ties the original selling price to the new selling price through the condition that profit doubles. The given relationship between the original marked price and cost allows us to express profit in terms of the original selling price and then scale it by the specified 16.66% increase.

Given Data / Assumptions:

• Original MP = Rs 400, which is 33.33% above cost ⇒ CP = 400 / (1 + 1/3) = 300
• Let original SP = S; new SP = S * (1 + 1/6) = (7/6)S
• Profit doubles: (New SP − CP) = 2 * (Original SP − CP)

Concept / Approach:
Form the doubling equation with CP = 300 and solve for S, then compute the increased SP.

Step-by-Step Solution:
(7/6)S − 300 = 2(S − 300)(7/6)S − 300 = 2S − 600(7/6 − 2)S = −300 ⇒ (−5/6)S = −300 ⇒ S = 360Increased SP = (7/6) * 360 = 420

Verification / Alternative check:
Original profit = 360 − 300 = 60; new profit = 420 − 300 = 120 (double), as required.

Why Other Options Are Wrong:
240/360 too low; 600 too high relative to the doubling condition.

Common Pitfalls:
Adding 25% and 16.66% directly; confusing profit doubling on CP with a standalone % change in SP.

Final Answer:
420