Comparative percentage: income difference framed correctly: Mukul’s income is 10% more than Sunil’s income. By what percent is Sunil’s income less than Mukul’s income?

Introduction / Context:
A classic comparison trap: “A is 10% more than B” is not symmetric with “B is 10% less than A.” The percent decrease from the larger reference is different because the base changes. This question assesses understanding of base dependence in percentage comparisons.

Given Data / Assumptions:

• Mukul’s income M = 1.10 * Sunil’s income S.
• We must find the percentage by which S is less than M, i.e., (M − S)/M * 100%.

Concept / Approach:
Set S = 100 units for simplicity. Then M = 110. The difference is 10. Express the difference as a percentage of M (the larger base) since the question asks “how much less than Mukul’s.” This yields a non-intuitive 9.09% instead of 10%.

Step-by-Step Solution:

Verification / Alternative check:
Algebraic: If M = 1.10S, then (M − S)/M = (0.10S)/(1.10S) = 1/11 = 9.09%.

Why Other Options Are Wrong:
10% mistakenly uses Sunil’s base; 8.09%, 7.90%, 7.09% are arbitrary and do not match the correct ratio 1/11.

Common Pitfalls:
Using the same percent in reverse. Always pay attention to the requested reference base for “more than” versus “less than.”

Final Answer:
9.09%