A shopkeeper marked his goods at X% above their cost price and sold them at a discount of 10%. If he gained 71% profit, then find the value of X.

Correct option is D

Given:

A shopkeeper marked his goods at X% above their cost price and sold them at a discount of 10%. He gained 71% profit.

Formula used:
SP = CP × (1 + Profit%)
SP = MP × (1 - Discount%)

Solution:

Let the cost price (CP) = ₹100

Marked price (MP) = ₹(100 + X)
Discount = 10%

Selling price (SP) = ₹(MP × 90/100)
SP = 100 × (1 + 71/100) = SP = ₹171

SP = MP × (1 - Discount%
171 = (100 + X) × 90/100
171 × 100 = (100 + X) × 90
17100 = 90 × (100 + X)
17100 - 9000 = 90X
8100 = 90X
X = 90