A retailer buys 20 kg of tea at a 10% discount on the marked price, and also gets 1 kg free on purchasing 20 kg. He sells the entire stock at the marked price. Find his profit percentage.

Introduction:
This combines a price discount with a quantity bonus. The retailer’s cost is reduced by the discount, and his saleable quantity is increased by the free units. Selling at MRP yields a clean profit computation.

Given Data / Assumptions:

• Marked price per kg = M
• Buys 20 kg at 10% off → cost = 20 * 0.9M = 18M
• Gets 1 kg free → total quantity to sell = 21 kg
• Sells all at MRP → revenue = 21M

Concept / Approach:
Profit% is computed on cost: (Revenue − Cost)/Cost * 100. Using symbolic M cancels unknowns neatly.

Step-by-Step Solution:
Profit = 21M − 18M = 3MProfit% = 3M / 18M * 100 = 16.666...%

Verification / Alternative check:
Even with any absolute M, the ratio remains 1/6 due to proportionality.

Why Other Options Are Wrong:
12% and 14.28% understate; 30% overstates as if both benefits compounded differently.

Common Pitfalls:
Forgetting to include the free quantity in revenue potential; treating 10% off as 10% of selling price.

Final Answer:
16.66%