What is the standard formula used to calculate IQ?

• A. (Chronological age / Mental age) × 100
• B. (Mental age / Chronological age) × 100
• C. (Mental age × Chronological age) ÷ 100
• D. (Chronological age − Mental age) × 100

Answer: (B)

IQ measures how a person’s cognitive development compares to what is typical for their actual age. Mental age represents the level of performance characteristic of a certain age, while chronological age is the person’s real age. The standard formula uses the ratio of mental age to chronological age, multiplied by 100, so that when someone’s mental age matches their actual age, the IQ is 100. If mental age is higher than chronological age, the IQ exceeds 100; if lower, it’s below 100. The factor of 100 simply scales the result to a convenient, familiar range. Historically, this is how IQ was defined in early tests like the Stanford-Binet, though modern assessments often use a deviation-based approach. The other options don’t align with the intended interpretation: inverting the ratio would flip the meaning (higher cognitive development would yield a higher IQ only if the ratio is MA/CA, not CA/MA), and using a product or a difference produces a value that doesn’t reflect the standard relationship between MA and CA.