Find the simple interest on ₹5,000 at 8% per annum for 3 years.

₹1,200. SI = P R T100 = 5000 8 3100 = ₹1,200.

At what rate percent per annum will ₹800 amount to ₹920 in 3 years at simple interest?

5%. SI = 920 - 800 = ₹120. R = 100 120800 3 = 5\%.

A sum of money doubles itself in 8 years at simple interest. In how many years will it become four times itself?

24. Doubling means the interest equals the principal in 8 years. To become four times, the interest must be 3P, which takes 3 8 = 24 years.

The simple interest on a sum for 4 years at 6% per annum is ₹1,200. What is the principal?

₹5,000. P = 100 SIR T = 100 12006 4 = ₹5,000.

₹12,000 is lent partly at 10% and partly at 8% simple interest. The total interest for one year is ₹1,100. How much was lent at 10%?

₹7,000. Let ₹x be lent at 10%. Then 0.10x + 0.08(12000 - x) = 1100, i.e. 0.02x + 960 = 1100, so x = ₹7,000.

AI-guided practice

Quantitative Aptitude · Commercial Maths

Simple Interest — Questions & Answers

Simple interest is charged only on the original principal, so it grows linearly with time. Every question is one rearrangement of a single formula.

5 solved questions
·
Step-by-step AI walkthroughs
·
Key formulas included

Key formulas

$SI = \dfrac{P \times R \times T}{100}$ ; amount $A = P + SI$
$P = \dfrac{100 \times SI}{R \times T}$ , $\;R = \dfrac{100 \times SI}{P \times T}$ , $\;T = \dfrac{100 \times SI}{P \times R}$
A sum becomes $n$ times itself in $T = \dfrac{100\,(n-1)}{R}$ years

5 solved Simple Interest questions

Try each question first — tap an option to check your answer, or open Learn step by step for a guided walkthrough.

01
Find the simple interest on ₹5,000 at 8% per annum for 3 years.
4 steps · reveal one at a time
1. Step 1: Identify Given Values
  Start by noting down the given information from the question. The Principal (P) is ₹5,000, the Rate (R) is 8% per annum, and the Time (T) is 3 years.
2. Step 2: Recall Simple Interest Formula
  The formula to calculate Simple Interest (SI) is $SI = \dfrac{P \times R \times T}{100}$ . This formula helps us find the interest earned on the principal amount over a specific period.
3. Step 3: Calculate the Interest
  Now, substitute the identified values into the formula. We have $SI = \dfrac{5000 \times 8 \times 3}{100}$ . Multiply the numbers in the numerator and then divide by 100 to get the simple interest.
4. Step 4: The answer
  So the answer is (B) ₹1,200. After calculating, $SI = \dfrac{120000}{100} = 1200$ , which matches option (B).
02
At what rate percent per annum will ₹800 amount to ₹920 in 3 years at simple interest?
4 steps · reveal one at a time
1. Step 1: Calculate Simple Interest
  The simple interest (SI) is the difference between the final amount and the principal amount. In this case, the principal is ₹800 and the amount is ₹920. So, $SI = Amount - Principal = 920 - 800 = \text{\text{Rs}\,}120$ .
2. Step 2: Apply Rate Formula
  Now we use the formula for the rate of simple interest: $R = \frac{SI \times 100}{P \times T}$ . We know $SI = \text{\text{Rs}\,}120$ , $P = \text{\text{Rs}\,}800$ , and $T = 3$ years. Substitute these values into the formula.
3. Step 3: Calculate the Rate
  Substitute the values: $R = \frac{120 \times 100}{800 \times 3}$ . This simplifies to $R = \frac{12000}{2400} = 5$ . So, the rate of interest is $5\%$ per annum.
4. Step 4: The answer
  So the answer is (A) 5%. This rate ensures that ₹800 grows to ₹920 in 3 years with simple interest.
03
A sum of money doubles itself in 8 years at simple interest. In how many years will it become four times itself?
5 steps · reveal one at a time
1. Step 1: Understand "doubling"
  When a sum of money doubles itself, it means the interest earned ( $I$ ) is exactly equal to the original principal amount ( $P$ ). So, $I = P$ .
2. Step 2: Time for doubling
  The problem states that the money doubles in 8 years. This tells us that it takes 8 years to earn an interest amount equal to the principal ( $P$ ). So, $I = P$ in $T = 8$ years.
3. Step 3: Goal: four times
  We want the money to become four times itself. This means the total amount will be $4P$ . For this to happen, the interest earned must be $4P - P = 3P$ .
4. Step 4: Calculate total time
  Since an interest of $P$ is earned in 8 years, an interest of $3P$ will take $3$ times as long. So, the time required is $3 \times 8 = 24$ years.
5. Step 5: The answer
  So the answer is (C) 24, because it takes 24 years for the interest to become three times the principal, making the total amount four times the principal.
04
The simple interest on a sum for 4 years at 6% per annum is ₹1,200. What is the principal?
4 steps · reveal one at a time
1. Step 1: Understand the problem
  We are given the Simple Interest ( $SI = \text{\text{Rs}\,}1,200$ ), the Time ( $T = 4$ years), and the Rate ( $R = 6\%$ per annum). Our goal is to find the Principal ( $P$ ). We need a formula that connects these values.
2. Step 2: Recall the formula
  The standard formula for Simple Interest is $SI = \dfrac{P \times R \times T}{100}$ . To find the Principal ( $P$ ), we can rearrange this formula: $P = \dfrac{100 \times SI}{R \times T}$ . This will allow us to solve for P.
3. Step 3: Substitute and calculate
  Now, substitute the given values into the rearranged formula: $P = \dfrac{100 \times 1200}{6 \times 4}$ . First, calculate the denominator: $6 \times 4 = 24$ . Then, calculate the numerator: $100 \times 1200 = 120000$ . So, $P = \dfrac{120000}{24}$ .
4. Step 4: The answer
  So the answer is (B) ₹5,000. Dividing $120000$ by $24$ gives us $5000$ . Therefore, the principal amount is ₹5,000.
05
₹12,000 is lent partly at 10% and partly at 8% simple interest. The total interest for one year is ₹1,100. How much was lent at 10%?
5 steps · reveal one at a time
1. Step 1: Define the amounts
  Let the amount lent at 10% interest be $x$ . Since the total amount lent is ₹12,000, the amount lent at 8% interest will be $12000 - x$ .
2. Step 2: Calculate total interest
  The interest from the first part is $0.10x$ . The interest from the second part is $0.08(12000 - x)$ . The total interest for one year is ₹1,100.
3. Step 3: Formulate the equation
  We can set up an equation for the total interest: $0.10x + 0.08(12000 - x) = 1100$ . This equation represents the sum of interest from both parts.
4. Step 4: Solve for x
  Now, let's solve the equation: $0.10x + 960 - 0.08x = 1100$ . Simplify to $0.02x + 960 = 1100$ . Subtract 960 from both sides: $0.02x = 140$ . Finally, $x = 140 \div 0.02 = 7000$ .
5. Step 5: The answer
  So the answer is (C) ₹7,000. This is the amount that was lent at 10% interest, as defined by $x$ in our equation.

Free to start

Get exam-ready on Simple Interest

Generate fresh simple interest practice sets in Test Studio, get step-by-step AI explanations the moment you slip, and close the gaps in Socrative Mode.

Start practising free Browse all topics

Step-by-step AI solutions
Fresh practice sets on demand
Guided Socrative Mode drills

Key formulas

5 solved Simple Interest questions

Get exam-ready on Simple Interest

More in Commercial Maths