Simple Interest Questions

• Interest-rate hike and annual income increase: If the annual simple interest rate on an investment rises from 6.5% to 8%, a person’s yearly interest income increases by ₹ 4050. Find the invested capital (principal).
• Principal trebled midway — total simple interest over 10 years: The simple interest on a sum of money is ₹ 600 after 10 years. If the principal is tripled after 5 years (rate unchanged), what is the total simple interest at the end of 10 years?
• Split principal at 12% and 12.5% — find the 12% portion: A total of ₹ 2540 is lent in two parts, one at 12% p.a. and the other at 12.5% p.a. If the total annual interest is ₹ 311.60, how much is lent at 12%?
• Average rate planning across four parts — find the missing rate: ₹ 10000 is lent in four parts: ₹ 2000 at 8%, ₹ 4000 at 7.5%, ₹ 1400 at 8.5%, and the remainder at an unknown rate r. If the overall average rate is 8.13% p.a., what is r?
• When does simple interest equal the principal? If the simple interest for 5 years equals 40% of the principal, after how many years will the simple interest be equal to the principal itself?
• Find the principal — monthly simple interest rate: What principal will amount to ₹ 3400 in 3 years at a simple interest rate of 1% per month (i.e., 12% per annum)?
• Equalize simple interests — find the time: Simple interest on ₹ 1680 for 4 years at 7.5% per annum equals the simple interest on ₹ 1200 at 7% per annum for some time T. Find T.
• Doubling time under simple interest: If a sum of money becomes double at simple interest in 12 years, what is the annual rate of interest?
• Two-part lending at 8% and 10% — find the 8% portion: A sum of ₹ 4000 is lent out partly at 8% and partly at 10% simple interest. If the total annual interest is ₹ 352, how much was lent at 8%?
• Target average return via a two-rate mix: A man invests ₹ 3000 at the rate of 5% per annum. How much additional money should he invest at the rate of 8% per annum so that his overall annual return works out to exactly 6% per annum on the combined investment?
• Rate cut and withdrawal — back-solve original deposit: When a bank reduces its annual simple interest rate from 6.5% to 5.5%, a depositor withdraws ₹ 600. As a result, the depositor’s annual interest falls by ₹ 73. What was the original deposit amount before the withdrawal?
• Loan cleared with cash plus asset — price the cow: A farmer borrows ₹ 4200 at 10% per annum simple interest. After 5 years, he pays ₹ 5000 in cash and gives a cow to settle the account fully. What is the cost of the cow?
• Principal trebled after 5 years — total simple interest in 10 years: The simple interest on a sum of money is ₹ 600 after 10 years at a constant rate. If the principal is tripled after 5 years (rate unchanged), what will be the total interest by the end of the 10th year?
• Equal sums at 10% — unequal durations, known gap in interest: Two equal sums are lent at simple interest at 10% per annum, one for 4 years and the other for 5 years. If the difference between the interests is ₹ 220, find each sum.
• Staggered borrowings at 7.75% — compute total due: A man borrows ₹ 12000 for 4 years at 7.75% per annum simple interest. One year later, he borrows another ₹ 12000 for 3 years at the same rate. How much must he pay in total at the end to settle both loans?
• Rising yearly rates under simple interest — find principal: A loan runs for 5 years with simple interest rates of 7% in year 1 and increasing by 0.5% each subsequent year. If the total interest paid over the 5 years is ₹ 3690, how much was originally borrowed?
• Compound interest crediting frequency — yearly vs half-yearly for 1 year: What is the difference between the compound interest on ₹ 50000 at 12% per annum for one year when interest is credited yearly versus half-yearly?
• Simple Interest – Equal annual instalments on a loan: Vikram borrows ₹ 6,450 at a simple interest rate of 5% per annum. He agrees to repay the loan in 4 equal annual instalments (same rupee amount each year). What is the amount of the annual instalment he must pay?
• Simple Interest – Split lending at two rates: Subbarao has ₹ 2,540. He lends part at 12% per annum and the rest at 12.5% per annum. After one year, the total interest received is ₹ 311.60. How much did he lend at 12% per annum?
• Simple Interest – Fractional year at a given rate: At 8.5% per annum simple interest, how much interest will a principal of ₹ 5,800 earn in 2 years 3 months (i.e., 2.25 years)?