Eight years old Sudhir has a mental age of ten years. What is his I.Q.?

Concept: Intelligence Quotient (IQ) is defined as the ratio of a person's Mental Age (MA) to their Chronological Age (CA), expressed as a percentage: IQ = (MA / CA) × 100. It measures how far a person's mental development is ahead of or behind what is typical for their actual age.

Application:

1. Identify the given values: Mental Age (MA) = 10 years, Chronological Age (CA) = 8 years.

2. Write the IQ formula and substitute the values: IQ = (MA / CA) × 100 = (10 / 8) × 100.

3. Divide Mental Age by Chronological Age: 10 ÷ 8 = 1.25.

4. Multiply by 100 to express it as a quotient: 1.25 × 100 = 125.

Cross-check: Since Sudhir's mental age (10) is greater than his chronological age (8), the IQ must come out above 100 — which the computed value satisfies. Swapping the ratio (using CA / MA instead of MA / CA) would instead give a value below 100, which would contradict a child whose mental development is ahead of their age.

Result: Sudhir's I.Q. is 125.