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Tamil Nadu (TNBSE)Class 7 Mathematics★ 8-12 marks in the TN Class 7 Term 3 exam through percentage, profit/loss and interest sums

Percentage and Simple Interest

Samacheer Kalvi (TN State Board) Class 7 Maths — Term 3 Chapter 2, Percentage and Simple Interest. Converting between percentages, fractions and decimals, finding a percentage of a quantity, profit and loss percentages, and computing simple interest with the formula I = PNR/100, with worked examples, exercises and quick revision.

⏱ 15 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Convert between percentages, fractions and decimals
2Find a percentage of a quantity
3Compute profit and loss percentages on cost price
4Apply the simple interest formula
5Find the amount after interest

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Why this chapter matters

Percentages, profit and loss and simple interest are everyday money skills used in shopping, banking and business. These are high-weight, directly tested topics in the TN Class 7 Term 3 exam.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

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Term 1 — Direct and Inverse Proportion

Ratio and the unitary method.

Percentage and Simple Interest — Class 7 Maths (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 7 Mathematics, Term 3 — Chapter 2. Percentages, profit and loss, and simple interest.

1. About this chapter

This chapter covers percentages and their conversions, percentage of a quantity, profit and loss percentages, and simple interest.

2. Percentage and conversions

A percentage means "out of 100" — 25% = 25/100.
Percent → fraction: divide by 100 (40% = 40/100 = 2/5).
Percent → decimal: divide by 100 (40% = 0.4).
Fraction/decimal → percent: multiply by 100 (3/5 = 60%; 0.7 = 70%).
Percentage of a quantity: % × quantity (20% of 150 = 20/100 × 150 = 30).

3. Profit and loss percentages

Profit = SP − CP (when selling price > cost price); Loss = CP − SP.
Profit % = (Profit ÷ CP) × 100; Loss % = (Loss ÷ CP) × 100 (always on the cost price).
Example: CP = ₹200, SP = ₹250 → Profit ₹50 → Profit % = 50/200 × 100 = 25%.

4. Simple interest

When money (the principal P) is lent or borrowed at a rate R% per year for N years, the simple interest is:

I = (P × N × R) ÷ 100

The amount A = P + I.
Example: P = ₹1000, R = 5%, N = 2 years → I = 1000 × 2 × 5 ÷ 100 = ₹100; A = ₹1100.

5. Worked examples

Example 1. Convert 3/4 to a percentage. 3/4 × 100 = 75%.

Example 2. A shopkeeper buys a bag for ₹400 and sells it for ₹460. Find the profit %. Profit = 60 → 60/400 × 100 = 15%.

Example 3. Find the simple interest on ₹2000 at 8% for 3 years. I = 2000 × 3 × 8 ÷ 100 = ₹480.

6. Exercises (Samacheer Kalvi)

Convert: (a) 45% to a fraction (b) 0.6 to a percent.
Find 15% of ₹600.
CP = ₹500, SP = ₹450. Find the loss and loss %.
Find the simple interest on ₹1500 at 10% per annum for 2 years.
Find the amount when ₹2500 is invested at 6% for 4 years.

7. Common mistakes

Mistake: Taking profit % on the selling price. Fix: Profit % and loss % are always on the cost price.
Mistake: Forgetting to divide by 100 in the interest formula. Fix: I = PNR/100.
Mistake: Reporting the interest as the amount. Fix: Amount = Principal + Interest.

8. Quick revision

Term 3 · Ch 2 · percentage and interest.
% means out of 100; convert via ÷100 or ×100.
Profit/Loss % = (profit or loss ÷ CP) × 100.
Simple interest I = PNR/100; Amount A = P + I.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Percentage of a quantity

(% ÷ 100) × quantity

Out of 100.

Profit / Loss %

(profit or loss ÷ CP) × 100

Always on cost price.

Simple interest

I = (P × N × R) ÷ 100

P principal, N years, R rate.

Amount

A = P + I

Principal plus interest.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Taking profit % on the selling price

✓ Profit % and loss % are always calculated on the cost price.

WATCH OUT

✗ Forgetting to divide by 100 in the interest formula

✓ I = PNR/100.

WATCH OUT

✗ Reporting the interest as the amount

✓ Amount = Principal + Interest.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Conversions and percentage of

Convert percentages and find percentages of quantities.

Questions

Profit and loss

Find profit/loss and their percentages.

Questions

Simple interest

Compute interest and amount.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Convert

Convert 3/4 to a percentage.

▶ Show solution

75%.

Q2EASY· Percentage of

Find 15% of ₹600.

▶ Show solution

₹90.

Q3MEDIUM· Profit/Loss

CP = ₹500, SP = ₹450. Find the loss and loss %.

▶ Show solution

Loss ₹50; loss % = 50/500 × 100 = 10%.

Q4MEDIUM· Simple interest

Find the simple interest on ₹1500 at 10% per annum for 2 years.

▶ Show solution

1500 × 2 × 10 ÷ 100 = ₹300.

Q5MEDIUM· Amount

Find the amount when ₹2500 is invested at 6% for 4 years.

▶ Show solution

I = 2500 × 4 × 6 ÷ 100 = ₹600; A = 2500 + 600 = ₹3100.

Q6EASY· Profit

CP = ₹200, SP = ₹250. Find the profit %.

▶ Show solution

Profit ₹50; profit % = 50/200 × 100 = 25%.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Term 3 Chapter 2 of Samacheer Kalvi Class 7 Maths.
•Percentage means out of 100; convert with ÷100 or ×100.
•Percentage of a quantity = (% ÷ 100) × quantity.
•Profit = SP − CP, Loss = CP − SP; profit/loss % is on the cost price.
•Simple interest I = PNR/100.
•Amount A = Principal + Interest.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 8-12 marks across percentage, profit/loss and interest

Question type	Marks each	Typical count	What it tests
Conversions	1	2-3	Percent ↔ fraction/decimal
Profit / loss	2	2	Percentage on cost price
Simple interest	2-3	2	Interest and amount

Prep strategy

Convert using ÷100 or ×100
Always base profit/loss % on the cost price
Memorise I = PNR/100
Add interest to principal for the amount

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Shopping

Discounts and offers are given as percentages.

Business

Profit and loss percentages measure performance.

Banking

Loans and savings earn simple (and compound) interest.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Show the conversion step for percentages
Base profit/loss % on CP
Write the interest formula before substituting
Give both interest and amount when asked

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Find the rate if ₹1000 earns ₹150 interest in 3 years.
An article sold at 20% profit fetched ₹600. Find its cost price.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 7 Term 3 ExamHigh

NMMS / Foundation MathsHigh

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Profit is the gain made on what you spent (the cost price), so the percentage must be measured against the cost price to show the true rate of gain.

P is the principal (money lent or borrowed), N is the time in years, R is the rate of interest per year as a percentage, and I is the simple interest earned.

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