The salary of A is 40% of the salary of B, and the salary of B is 25% of the salary of C. What percentage of the salary of C is the salary of A?

Introduction:
This problem tests chained percentage relationships between three quantities. Such questions are common in aptitude exams where salaries, prices, or marks of different people are related through percentages. The aim is to express everything in terms of a single base quantity and then derive the final percentage required.

Given Data / Assumptions:
Salary of A is 40% of salary of B.
Salary of B is 25% of salary of C.
We need to find salary of A as a percentage of salary of C.
All salaries are positive real numbers and there is no additional condition given, so we model them with variables.

Concept / Approach:
When there is a chain of percentage relations, it is often easiest to express all amounts in terms of one reference, here salary of C. We use the fact that percentage can be converted into decimal multipliers. For example, 40% becomes 0.40 and 25% becomes 0.25. Then we multiply the corresponding factors to connect A directly to C.

Step-by-Step Solution:
Let the salary of C be C. Given that salary of B is 25% of salary of C. So salary of B = 25% of C = 0.25 * C. Now salary of A is 40% of salary of B. So salary of A = 40% of B = 0.40 * B. Substitute B = 0.25 * C into this expression. Salary of A = 0.40 * (0.25 * C) = 0.10 * C. Therefore salary of A is 0.10 times salary of C. Convert 0.10 to percentage by multiplying by 100: 0.10 * 100 = 10%.
Verification / Alternative check:
We can use assumed numerical values to verify. Suppose salary of C is Rs. 100. Then salary of B is 25% of 100, which is Rs. 25. Salary of A is 40% of 25, which is Rs. 10. Now A as a percentage of C is 10 out of 100, that is 10%. This concrete example confirms the general algebraic result.

Why Other Options Are Wrong:
20%, 25%, 30%, and 40% all come from incorrect combinations of percentages. Someone might mistakenly add 40% and 25% or incorrectly apply percentages sequentially without multiplying the factors. The correct operation is multiplication of the percentage factors, not arithmetic addition or subtraction of those percentages.

Common Pitfalls:
Students sometimes treat 40% of 25% as 65% or 15% by adding or subtracting, which is incorrect. The correct method is to convert each percentage to decimal and multiply. Another pitfall is forgetting which quantity is a percentage of which, for example, confusing 25% of C with C being 25% of B. Reading the statements carefully and drawing a simple chain diagram can prevent these errors.

Final Answer:
Salary of A is 10% of the salary of C.