Simple & Compound Interest Aptitude Questions with Solutions
40 Simple & Compound Interest questions with hints, worked solutions and time targets — 13 easy · 18 medium · 9 hard.
- Section: Quantitative Aptitude
- Questions: 40
- By difficulty: 13 easy · 18 medium · 9 hard
- Cost: Free, unlimited on every plan
Growth over periods, the difference between SI and CI, and doubling times.
Simple & Compound Interest: the essentials
- Simple interest: SI = P × R × T/100, and the amount A = P(1 + RT/100). Every year earns the same interest.
- Under SI a sum becomes n times itself when R × T = 100(n − 1): doubling needs RT = 100, tripling RT = 200.
- Two SI amounts at different times differ by the interest for the gap, which gives the yearly interest at once.
- Compound interest: A = P(1 + R/100)ⁿ, and CI = A − P. Present value = A ÷ (1 + R/100)ⁿ.
- Half-yearly compounding: R/2 per period for 2n periods; quarterly: R/4 for 4n periods.
- Two years at R% compound is 2R + R²/100 per cent in all.
- CI − SI on P for 2 years = P(R/100)²; for 3 years = P(R/100)²(3 + R/100).
- Consecutive CI amounts give the rate directly: (A₂ − A₁)/A₁ × 100. Each year's interest exceeds the last by R% of it.
- Under CI the multiples are powers: doubling in t years means 4 times in 2t and 8 times in 3t.
- SI and CI are equal for the first year of annual compounding.
Multipliers worth memorising
1.1² = 1.21, 1.1³ = 1.331, 1.05² = 1.1025, 1.05³ = 1.157625, 1.2² = 1.44, 1.04² = 1.0816.
Example: on ₹4,000 at 15% for 2 years, CI − SI = 4,000 × (0.15)² = ₹90.
Questions
- Simple interest for four years Easy
What is the simple interest on ₹8,000 at 7.5% per annum for 4 years? - Compound interest for two years Easy
What is the compound interest on ₹10,000 at 10% per annum for 2 years, compounded annually? - Difference between CI and SI Medium
What is the difference between compound and simple interest on ₹5,000 at 8% per annum for 2 years? - Doubling in eight years Easy
At what rate of simple interest will a sum double itself in 8 years? - Working back to the principal Easy
A sum grows to ₹6,050 in 2 years at 10% per annum compound interest. What was the sum? - Compounded half-yearly Medium
What is the compound interest on ₹16,000 at 20% per annum for 1 year, compounded half-yearly? - Simple interest for three years Easy
What is the simple interest on ₹12,000 at 8% per annum for 3 years? - Principal from the interest Easy
A sum earns ₹1,750 as simple interest in 5 years at 7% per annum. What is the principal? - Rate from the interest Easy
At what rate of simple interest will ₹8,000 earn ₹1,920 in 4 years? - Time from the interest Easy
In how many years will ₹6,000 earn ₹1,800 as simple interest at 5% per annum? - Doubling under simple interest Medium
At what rate of simple interest does a sum double itself in 8 years? - Tripling under simple interest Medium
In how many years will a sum triple itself at 10% per annum simple interest? - From doubling to quadrupling Medium
A sum doubles itself in 10 years at simple interest. In how many years will it become four times itself? - Compound interest on ₹20,000 for two years Easy
What is the compound interest on ₹20,000 at 10% per annum for 2 years, compounded annually? - Compound interest for three years Easy
What is the amount on ₹10,000 at 10% per annum compound interest for 3 years? - The gap between CI and SI Medium
What is the difference between compound and simple interest on ₹8,000 at 10% per annum for 2 years? - Principal from the CI–SI gap Medium
The difference between compound and simple interest for 2 years at 5% per annum is ₹50. What is the principal? - ₹8,000 compounded half-yearly Medium
What is the compound interest on ₹8,000 at 20% per annum for 1 year, compounded half-yearly? - Compounded quarterly Hard
What is the amount on ₹10,000 at 8% per annum for 1 year, compounded quarterly? - Principal from ₹9,261 in three years Medium
A sum amounts to ₹9,261 in 3 years at 5% per annum compound interest. What was the principal? - From one year's amount to the next Hard
A sum at compound interest amounts to ₹4,410 in 2 years and ₹4,630.50 in 3 years. What is the rate of interest? - Two amounts under simple interest Hard
A sum amounts to ₹1,560 in 3 years and ₹1,680 in 5 years at simple interest. What is the principal? - A sum split into two investments Hard
₹2,600 is split into two parts, one lent at 10% and the other at 8% simple interest for one year. If the total interest is ₹230, what is the part lent at 10%? - A higher rate earns more Medium
A sum lent at a rate 3% higher would have earned ₹300 more in 4 years under simple interest. What is the sum? - Doubling under compound interest Medium
A sum doubles in 5 years at compound interest. In how many years will it become eight times itself? - Nine times under compound interest Medium
A sum triples in 4 years at compound interest. In how many years will it become nine times itself? - Two loans, one total Easy
A man lends ₹5,000 at 6% and ₹4,000 at 8% simple interest for 2 years. What is his total interest? - Amount after simple interest Easy
What amount will ₹15,000 grow to in 4 years at 9% per annum simple interest? - Compound growth of a deposit Medium
A deposit of ₹6,250 grows at 4% per annum compound interest. What is the amount after 2 years? - Interest as a fraction of the principal Hard
A sum becomes 9/8 of itself in 3 years at simple interest. What is the rate of interest? - Two sums, equal after different times Easy
₹1,000 is lent at 5% simple interest. After how many years will the amount be ₹1,400? - Interest in the second year Medium
The compound interest for the first year on a sum at 10% per annum is ₹500. What is the interest for the second year? - Borrowing cheap and lending dear Medium
A man borrows ₹5,000 at 4% simple interest and lends it at 6% for 3 years. What is his total gain? - Same sum, two periods Hard
The simple interest on a sum for 3 years at 8% exceeds that for 2 years at 5% by ₹280. What is the sum? - Two-year effective rate Medium
What single percentage is equivalent to compound interest at 20% per annum for 2 years? - Equal annual instalments Hard
A sum of ₹1,000 is to be repaid in two equal annual instalments at 5% simple interest on the outstanding amount. What is each instalment, to the nearest rupee? - Interest for one and a half years Hard
What is the amount on ₹8,000 at 10% per annum compound interest for 1½ years, compounded half-yearly? - Rate changing over the years Medium
A sum of ₹10,000 earns simple interest at 5% for the first 2 years, 8% for the next 3 years and 10% thereafter. What is the total interest after 7 years? - The three-year gap Hard
The difference between compound and simple interest on a sum for 3 years at 10% per annum is ₹93. What is the sum? - When simple and compound agree Medium
For which period are the simple and compound interest on the same sum at the same rate exactly equal?
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