A trader sells sugar at Rs 400 for 20 kg (i.e., Rs 20 per kg). A customer negotiates 20% price discount, but the trader short-weighs by 4% per kg delivered. What is the customer’s effective discount percentage versus the original list price per actual kg?

Introduction:
When both price and quantity change, compute the effective price per actual kilogram delivered. Short weight reduces the benefit of the price discount.

Given Data / Assumptions:

• Original price = Rs 20 per kg.
• Discounted billed price = 20% off ⇒ Rs 16 per billed kg.
• Short weight = 4% ⇒ actual delivery per billed kg = 0.96 kg.

Concept / Approach:
Effective price per actual kg = billed price / actual quantity delivered. Effective discount% compares this with the original Rs 20 per actual kg.

Step-by-Step Solution:
Effective price per actual kg = 16 / 0.96 = 16.666...Effective discount% = (20 − 16.666...)/20 * 100 = 16.666...%

Verification / Alternative check:
If the customer pays Rs 16 for 0.96 kg, scaling to 1 kg costs 16.666..., which is 1/6 less than 20, i.e., 16 2/3%.

Why Other Options Are Wrong:

• 16% / 15.5% / 19.6%: each miscomputes the base or mixes up the order of changes.

Common Pitfalls:

• Applying the 4% to the price instead of to the weight delivered.

Final Answer:
16.66 %