© 2026 LearnInShort
Why Interest Questions Are Guaranteed Marks
Every quantitative paper carries two or three interest questions, and they are pure formula work — no reasoning, no trick reading. Learn four formulas and you never lose these marks again.
Simple Interest (SI) is calculated on the original principal every single year. The money you earn does not itself start earning.
> SI = (P x R x T) / 100 and Amount = P + SI
Here P is the principal, R the rate per cent per annum, T the time in years.
Example: Rs 6,000 at 8% for 3 years.
SI = (6000 x 8 x 3)/100 = Rs 1,440. Amount = Rs 7,440.
Notice the interest is Rs 480 in year one, Rs 480 in year two, Rs 480 in year three — identical, because the base never changes. That fixed base is the entire difference between SI and CI, and every trap in this chapter grows out of it.
1. Find the simple interest on Rs 6,000 at 8% per annum for 3 years.
2. What is the compound interest on Rs 5,000 at 10% per annum for 2 years, compounded annually?
3. The difference between the compound interest and the simple interest on a sum of Rs 10,000 at 5% per annum for 2 years is:
4. A sum of money doubles itself in 8 years at simple interest. What is the rate of interest per annum?
5. Find the compound interest on Rs 8,000 for 1 year at 20% per annum, compounded half-yearly.
6. The difference between compound interest and simple interest on Rs 16,000 at 5% per annum for 3 years is:
7. At what rate of simple interest per annum will Rs 1,200 amount to Rs 1,560 in 3 years?
8. The compound interest on a certain sum for 2 years at 10% per annum is Rs 630. What is the sum?