A boy was asked to multiply a number by 12, but he multiplied it by 21 and got an answer 63 more than the correct answer. What was the number?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 7
Multiplying by 21 instead of 12 adds \(21-12=9\) times the number to the result, and this extra amount is 63.
Let the number be \(x\)
\(21x-12x=63\)
\(9x=63\), so \(x=7\)
Check: \(147-84=63\). The number was 7.