In how many years will a sum of Rs 800 become Rs 1040 at 6% per annum simple interest?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 5 years
The interest is the amount minus the sum, and simple interest grows by the same amount every year.
Interest \(=1040-800=240\)
Interest for 1 year \(\displaystyle =\frac{800\times6}{100}=48\)
Time \(=240\div48=5\) years
The time is 5 years.
Why the other options are incorrect
Option (1) 4 years — Incorrect. In 4 years the interest is \(\displaystyle\frac{800\times6\times4}{100}=192\), so the sum becomes Rs 992, not Rs 1040.
Option (2) 3 years — Incorrect. In 3 years the interest is \(\displaystyle\frac{800\times6\times3}{100}=144\), so the sum becomes Rs 944, not Rs 1040.
Option (4) 6 years — Incorrect. In 6 years the interest is \(\displaystyle\frac{800\times6\times6}{100}=288\), so the sum becomes Rs 1088, not Rs 1040.