Simple Interest Questions: Formula, Solved Examples and Practice Problems

Simple interest questions help students learn how to calculate interest on borrowed or invested money using the simple interest formula. Practising simple interest problems with solutions improves calculation skills and builds confidence in solving real-life questions related to loans, savings, investments and banking.

In this article, you'll learn the simple interest formula, step-by-step solving methods, solved examples, and practice questions to improve your understanding and exam preparation.

Table of Contents

• Simple Interest Formula
• Solved Examples of Simple Interest
• Practice Questions on Simple Interest
• Frequently Asked Questions on Simple Interest Questions

 

Simple Interest Formula

The formula for simple interest in mathematics is:

Simple Interest (SI) = (P × R × T) / 100

Where:

• P = Principal (original amount of money)

• R = Rate of interest per annum (in %)

• T = Time (in years)

How to Solve Simple Interest Questions (Steps)

Follow the steps below to calculate the Simple Interest (SI).

Step 1: Identify the given values: Principal (P), Rate (R), and Time (T) from the question.

Step 2: Write the Simple Interest formula: SI = (P × R × T) / 100

Step 3: Put the values of P, R, and T in their respective places.

Step 4: Multiply P × R × T, then divide by 100.

Step 5: Write the final answer with proper unit (Rs.)

Example: Find the simple interest on Rs. 1,000 at 5% per annum for 2 years.

Solution:
Step 1: Write the formula
SI = (P × R × T) / 100

Step 2: Substitute the values
SI = (1000 × 5 × 2) / 100

Step 3: Simplify
SI = 10000 / 100

Step 4: Final Answer
SI = Rs. 100

Answer: The simple interest is Rs. 100.

Solved Examples of Simple Interest Questions

Easy Level Solved Examples

Question 1: Find the simple interest on Rs. 1,000 at 5% per annum for 2 years.
Solution:
SI = (P × R × T) / 100
SI = (1000 × 5 × 2) / 100 = Rs. 100

Question 2: Calculate the simple interest on Rs. 2,500 at 4% per annum for 3 years.
Solution:
SI = (P × R × T) / 100
SI = (2500 × 4 × 3) / 100 = Rs. 300

Question 3: A sum of Rs. 800 is invested at 10% per annum for 1 year. Find the interest.
Solution:
SI = (P × R × T) / 100
SI = (800 × 10 × 1) / 100 = Rs. 80

Question 4: Find the interest on Rs. 1,200 at 6% per annum for 2 years.
Solution:
SI = (P × R × T) / 100
SI = (1200 × 6 × 2) / 100 = Rs. 144

Question 5: What is the simple interest on Rs. 3,000 at 5% per annum for 1 year?
Solution:
SI = (P × R × T) / 100
SI = (3000 × 5 × 1) / 100 = Rs. 150

Medium Level Solved Examples 

Question 1: Find the total amount on Rs. 5,000 at 8% per annum for 2 years.
Solution:
SI = (5000 × 8 × 2) / 100 = Rs. 800
Amount = 5000 + 800 = Rs. 5,800

Question 2: A sum earns Rs. 600 as simple interest in 3 years at 5% per annum. Find the principal.
Solution:
SI = (P × R × T) / 100
P = (SI × 100) / (R × T)
P = (600 × 100) / (5 × 3) = Rs. 4,000

Question 3: At what rate will Rs. 2,000 earn Rs. 400 in 4 years?
Solution:
SI = (P × R × T) / 100
R = (SI × 100) / (P × T)
R = (400 × 100) / (2000 × 4) = 5%

Question 4: How long will it take for Rs. 1,500 to earn Rs. 450 at 6% per annum?
Solution:
SI = (P × R × T) / 100
T = (SI × 100) / (P × R)
T = (450 × 100) / (1500 × 6) = 5 years

Question 5: Find the simple interest on Rs. 4,000 at 7.5% per annum for 3 years.
Solution:
SI = (P × R × T) / 100
SI = (4000 × 7.5 × 3) / 100 = Rs. 900

Advanced Level Solved Examples 

Question 1: A sum becomes Rs. 6,600 in 2 years at 10% per annum. Find the principal.
Solution:
Amount = P + SI
SI = (P × 10 × 2) / 100 = 0.2P
So, Amount = P + 0.2P = 1.2P
1.2P = 6600 ⇒ P = Rs. 5,500

Question 2: Find the rate if Rs. 3,000 amounts to Rs. 3,900 in 5 years.
Solution:
SI = 3900 − 3000 = Rs. 900
R = (900 × 100) / (3000 × 5) = 6%

Question 3: A person invests Rs. 2,500 for 3 years and gets Rs. 600 as interest. Find the rate.
Solution:
SI = (P × R × T) / 100
R = (600 × 100) / (2500 × 3) = 8%

Question 4: In how many years will Rs. 2,000 become Rs. 3,200 at 10% per annum?
Solution:
SI = 3200 − 2000 = Rs. 1200
T = (1200 × 100) / (2000 × 10) = 6 years

Question 5: The difference between the amounts of Rs. 5,000 for 2 years and 4 years is Rs. 600. Find the rate.
Solution:
Extra time = 2 years
Interest for 2 years = Rs. 600
SI = (P × R × T) / 100
600 = (5000 × R × 2) / 100
600 = 100R
R = 6%

Practice Questions on Simple Interest

1. Find the simple interest on Rs. 2,500 at 4% per annum for 3 years.
2. A sum of Rs. 6,000 is invested at 5% per annum for 2 years. Calculate the interest earned.
3. How much interest will Rs. 1,200 earn in 5 years at 3% per annum?
4. If the simple interest on Rs. 4,000 for 2 years is Rs. 320, find the rate of interest.
5. How long will it take for Rs. 3,000 to earn Rs. 450 at 5% per annum?
6. A sum amounts to Rs. 5,600 in 4 years at 5% simple interest. Find the principal.
7. What rate of interest will turn Rs. 2,000 into Rs. 2,400 in 5 years under simple interest?
8. Find the total amount when Rs. 3,500 is invested at 6% per annum for 3 years.
9. A person earns Rs. 900 as interest on a sum in 3 years at 6% per annum. Find the principal.
10. In how many years will Rs. 1,500 amount to Rs. 1,950 at 10% simple interest?

Read more:

• Compound Interest Questions
• Compound Interest
• Profit and Loss Questions
• Percentage Questions

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