Simple interest problems: Class 7 practice
Simple interest is charged only on the original principal: SI = P × R × T ÷ 100, and Amount = P + SI.. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Percentages
- Multiplication
The idea behind simple interest problems
Simple interest is charged only on the original principal: SI = P × R × T ÷ 100, and Amount = P + SI.
Step-by-step method
- Identify P (₹), R (% per year), T (years).
- SI = PRT/100.
- Amount = P + SI.
- To find R or T, rearrange the same formula.
Worked example 1 (Basic)
Find the simple interest and amount on ₹2400 at 8% per year for 2 years.
- SI = 2400 × 8 × 2 ÷ 100 = ₹384
- Amount = 2400 + 384 = ₹2784
- Answer: SI = ₹384, Amount = ₹2784
Worked example 2 (Standard)
Find the simple interest and amount on ₹500 at 6% per year for 4 years.
- SI = 500 × 6 × 4 ÷ 100 = ₹120
- Amount = 500 + 120 = ₹620
- Answer: SI = ₹120, Amount = ₹620
Worked example 3 (Challenge)
₹5200 becomes ₹5616 in 2 years at simple interest. Find the rate.
- SI = 5616 − 5200 = ₹416
- R = (100 × 416) ÷ (5200 × 2) = 4%
- Answer: 4% per year
Common mistakes and misconceptions
- Using months as years
- Reporting SI when the amount is asked
Practice questions
- (Basic) Find the simple interest and amount on ₹600 at 6% per year for 5 years.
- (Basic) Find the simple interest and amount on ₹3600 at 10% per year for 2 years.
- (Standard) Find the simple interest and amount on ₹3500 at 4% per year for 4 years.
- (Standard) Find the simple interest and amount on ₹1100 at 4% per year for 3 years.
- (Challenge) ₹500 becomes ₹620 in 2 years at simple interest. Find the rate.
- (Challenge) ₹600 becomes ₹690 in 3 years at simple interest. Find the rate.
Answer key with full working
- Q1: SI = 600 × 6 × 5 ÷ 100 = ₹180 → Amount = 600 + 180 = ₹780 → Answer: SI = ₹180, Amount = ₹780
- Q2: SI = 3600 × 10 × 2 ÷ 100 = ₹720 → Amount = 3600 + 720 = ₹4320 → Answer: SI = ₹720, Amount = ₹4320
- Q3: SI = 3500 × 4 × 4 ÷ 100 = ₹560 → Amount = 3500 + 560 = ₹4060 → Answer: SI = ₹560, Amount = ₹4060
- Q4: SI = 1100 × 4 × 3 ÷ 100 = ₹132 → Amount = 1100 + 132 = ₹1232 → Answer: SI = ₹132, Amount = ₹1232
- Q5: SI = 620 − 500 = ₹120 → R = (100 × 120) ÷ (500 × 2) = 12% → Answer: 12% per year
- Q6: SI = 690 − 600 = ₹90 → R = (100 × 90) ÷ (600 × 3) = 5% → Answer: 5% per year
Syllabus note
This skill is listed under "Comparing Quantities" for Class 7 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is simple interest problems in?
"Comparing Quantities", Class 7 Maths (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.