At a discount of 13%, the selling price of an oven is Rs 18,000. If the shop keeps the same marked price and instead offers a discount of 27.5%, what will be the new selling price of the oven?

Introduction / Context:
This percentage based question tests the idea of moving from selling price back to marked price and then finding a new selling price under a different discount rate. Such questions are very common in aptitude exams and competitive tests where candidates must be comfortable reversing percentage calculations and applying successive discounts.

Given Data / Assumptions:
Selling price with 13 percent discount = Rs 18000. Discount rate 1 = 13 percent. Discount rate 2 = 27.5 percent. Marked price of the oven remains the same in both cases. All prices are in rupees and there are no additional taxes or charges.

Concept / Approach:
The selling price after a discount is calculated as marked price multiplied by (100 minus discount percent) divided by 100. To move backwards, we divide the selling price by this fraction to get the marked price. Once we know the marked price, we can again apply the new discount rate to compute the new selling price.

Step-by-Step Solution:
Let the marked price be M. With a 13 percent discount, selling price = M * (1 - 13/100) = M * 0.87. Given M * 0.87 = 18000. So M = 18000 / 0.87. Compute M: 18000 / 0.87 = 20689.655172 approximately. Now new discount rate = 27.5 percent, so new selling price = M * (1 - 27.5/100) = M * 0.725. New selling price = 20689.655172 * 0.725 which equals exactly 15000 when calculated accurately. Therefore the new selling price is Rs 15000.

Verification / Alternative check:
We can avoid dealing with the decimal by using ratios. Since 18000 corresponds to 87 percent of the marked price, 1 percent equals 18000 / 87. The new selling price should be 72.5 percent of the marked price. So new selling price = 72.5 * 18000 / 87. Multiplying 72.5 and 18000 and then dividing by 87 again gives 15000, which confirms the earlier calculation.

Why Other Options Are Wrong:
18000 is closer to 15000 than to 10875 or 12288.75 when discount increases, so options with very low values underestimate the effect. Values like 16638.75 or 13500 do not match the precise ratio 72.5/87 derived from the discount change. The exact computation gives 15000, so all other options are numerically inconsistent with the given data.

Common Pitfalls:
A frequent mistake is to apply both discounts directly to 18000 instead of going back to marked price. Another error is to treat the difference in discount percentages, 27.5 minus 13, as if it could be applied directly to the old selling price. Both shortcuts lead to incorrect results, because percentage discounts must always be applied on the marked price, not on the already reduced selling price.

Final Answer:
The new selling price of the oven when the shop offers a 27.5 percent discount instead of 13 percent is Rs 15000.