The marked price of a chair is Rs. 550. If a discount of 20% is allowed on the marked price, what is the selling price of the chair in rupees?

Introduction / Context:
This is a basic discount and selling price question involving a single article, a chair. The shopkeeper reduces the price of the chair by a given percentage of the marked price and we must compute the final selling price after the discount. Such questions commonly appear at the introductory level of profit, loss and discount topics in aptitude tests.

Given Data / Assumptions:

• Marked price (MP) of the chair = Rs. 550.
• Discount offered = 20% of the marked price.
• We must find the selling price after allowing this discount.

Concept / Approach:
The discount amount is calculated as a percentage of the marked price. The selling price is then the difference between the marked price and the discount amount. Mathematically: Discount = (discount rate / 100) * MP, and Selling price = MP − Discount. Alternatively, we can multiply the marked price directly by (1 − discount rate) to get the selling price.

Step-by-Step Solution:
Marked price MP = Rs. 550. Discount rate = 20%. Discount amount = (20 / 100) * 550. 20 / 100 = 0.20. Discount amount = 0.20 * 550 = Rs. 110. Selling price SP = MP − Discount. SP = 550 − 110 = Rs. 440.

Verification / Alternative check:
Instead of first finding the discount, we could directly calculate 80% of the marked price because selling price after a 20% discount is 100% − 20% = 80% of MP. Then SP = 0.80 * 550 = 440, giving the same result. This confirms that the calculation is consistent and correct.

Why Other Options Are Wrong:
430 and 420: These represent larger discounts than 20% and would correspond to discount rates higher than 20% if checked numerically.
470: This would correspond to a discount of only Rs. 80, which is less than 20%.
390: This is far below the correct price and corresponds to a discount greater than 28% of the marked price.

Common Pitfalls:
Some students mistakenly subtract 20 rupees instead of 20% or miscalculate 20% of 550. Another error is to directly subtract 20% from 550 as if it were a fixed amount, not realizing that percentages always refer to parts of the base value. Writing out the step of computing discount as 0.20 * 550 helps avoid confusion.

Final Answer:
The selling price of the chair after allowing a 20% discount is Rs. 440.