Chapter 2 of 16

13%

Tamil Nadu (TNBSE)Class 6 Mathematics★ 5-9 marks in the TN Class 6 Term 1 exam through expression-writing and simple equation sums

Introduction to Algebra

Samacheer Kalvi (TN State Board) Class 6 Maths — Term 1 Chapter 2, Introduction to Algebra. Constants and variables, writing algebraic expressions, using a variable to describe patterns, and forming and solving simple linear equations from word problems, with worked examples, exercises and quick revision.

⏱ 14 min readEasy difficulty✓ Free · NCERT-aligned

Worksheet

Podcast

Listen as a conversation

A teacher & a student talk through the chapter — in your language.

Mind Map

The chapter at a glance

Every concept and exam-favourite branch — revisable in 5 minutes.

…

Study Guide

Night-before notes

Key points, glossary and the questions most likely to show up.

…

VocabularyBuild your vocabularyLexiGenome mines the key words and schedules them with spaced repetition.Mine words →

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

1Distinguish constants and variables
2Write algebraic expressions from words
3Use a variable to describe a pattern
4Form equations from situations
5Solve simple linear equations

💡

Why this chapter matters

Algebra introduces letters for numbers, the language of all higher mathematics. Writing expressions and solving simple equations are directly tested in the TN Class 6 Term 1 exam.

Before you start — revise these

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

🔗

Class 5 — Patterns

Number patterns.

Introduction to Algebra — Class 6 Maths (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 6 Mathematics, Term 1 — Chapter 2. Using letters to stand for numbers.

1. About this chapter

This chapter introduces constants and variables, algebraic expressions, using a variable to describe patterns, and forming and solving simple linear equations from word problems.

2. Constants and variables

A constant has a fixed value (like 5 or 12).
A variable is a letter (x, y, n, a …) that can take different values.
An algebraic expression combines variables and constants with operations, e.g. x + 3, 2n, 5y − 1.

3. Using variables for patterns

A variable can describe a general rule. If a row has n tiles and there are 4 rows, the total is 4 × n = 4n.
The perimeter of a square of side s is 4s; the cost of n pens at ₹10 each is 10n.

4. Simple equations

An equation says two expressions are equal, e.g. x + 4 = 9.
Solve by finding the value of the variable that makes it true — do the same operation on both sides: x + 4 = 9 → x = 9 − 4 = 5.

5. Worked examples

Example 1. Write an expression for "7 more than a number x". x + 7.

Example 2. A box has b balls. Write the total in 5 such boxes. 5b.

Example 3. Solve x − 3 = 8. x = 8 + 3 = 11.

6. Exercises (Samacheer Kalvi)

State whether each is a constant or a variable: 9, x, 25, m.
Write an expression for: (a) 4 less than y (b) twice a number n (c) the cost of k books at ₹50 each.
The age of Ravi is x years. Write his age after 6 years.
Solve: (a) x + 5 = 12 (b) 3x = 18 (c) x − 7 = 2.
The perimeter of a square of side a is given by which expression?

7. Common mistakes

Mistake: Writing 2 × n as "2n" but reading it as "2 + n". Fix: 2n means 2 × n (multiplication), not addition.
Mistake: Changing only one side of an equation. Fix: Do the same operation on both sides.
Mistake: Confusing a variable with a fixed number. Fix: A variable can take many values; a constant is fixed.

8. Quick revision

Term 1 · Ch 2 · introduction to algebra.
Constant = fixed value; variable = a letter that can change.
Expression combines variables and constants (x + 3, 2n, 5y − 1); 2n means 2 × n.
Solve equations by doing the same operation on both sides.

Key formulas & results

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

Constant vs variable

fixed value vs a letter that can change

x, y, n are variables.

Expression

variables + constants with operations

2n means 2 × n.

Pattern rule

perimeter of square = 4s; cost = 10n

Variable describes a rule.

Solving equations

same operation on both sides

Find the variable's value.

⚠️

Common mistakes & fixes

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

WATCH OUT

✗ Reading 2n as 2 + n

✓ 2n means 2 × n (multiplication), not addition.

WATCH OUT

✗ Changing only one side of an equation

✓ Do the same operation on both sides.

WATCH OUT

✗ Confusing a variable with a fixed number

✓ A variable can take many values; a constant is fixed.

NCERT exercises (with solutions)

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

Constants and variables

Identify constants and variables.

Questions

Writing expressions

Translate words into expressions.

Questions

Solving equations

Solve simple linear equations.

Questions

Practice problems

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

Q1EASY· Expression

Write an expression for '7 more than a number x'.

▶ Show solution

x + 7.

Q2EASY· Expression

A box has b balls. Write the total in 5 such boxes.

▶ Show solution

5b.

Q3EASY· Identify

Which of these are variables: 9, x, 25, m?

▶ Show solution

x and m are variables; 9 and 25 are constants.

Q4EASY· Solve

Solve x − 3 = 8.

▶ Show solution

x = 11.

Q5MEDIUM· Solve

Solve 3x = 18.

▶ Show solution

x = 18 ÷ 3 = 6.

Q6EASY· Pattern

Write the perimeter of a square of side a.

▶ Show solution

4a.

5-minute revision

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

•Term 1 Chapter 2 of Samacheer Kalvi Class 6 Maths.
•A constant has a fixed value; a variable is a letter that can change.
•An expression combines variables and constants (x + 3, 2n, 5y − 1).
•2n means 2 × n, not 2 + n.
•A variable can describe a pattern (perimeter of a square = 4s).
•Solve equations by doing the same operation on both sides.

Tamil Nadu (TNBSE) marks blueprint

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

Typical chapter weightage: 5-9 marks across expressions and equations

Question type	Marks each	Typical count	What it tests
Objective	1	3-4	Constants/variables, expressions
Write expression	1-2	2	Words to expressions
Solve equation	2	1-2	Simple equations

Prep strategy

Translate key words into operations
Remember 2n means 2 × n
Keep equations balanced
Check the solution by substitution

Where this shows up in the real world

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

Formulas

Perimeter, area and cost rules are written with variables.

Problem solving

Unknowns in puzzles become variables to solve for.

Coding

Variables store and change values in programs.

Exam strategy

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

Underline key words to choose the operation
Write 2 × n as 2n
Balance both sides when solving
Verify by substituting the answer

Going beyond the textbook

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

Write a rule for the nth term of 3, 6, 9, 12 … using a variable.
Form and solve an equation: a number doubled and increased by 5 gives 17.

Where else this chapter is tested

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

TN Class 6 Term 1 ExamHigh

NMMS / Foundation MathsMedium

School unit testsHigh

AI helpers for this chapter

Generate more practice on the fly, or have the chapter explained at a different level.

⚡

Generate 5 more questions

Fresh MCQs + short-answer items based on this chapter, plus answer keys.

🧠

Explain at a different level

Re-explain the chapter at the level you actually want.

📝 My notes

Saved on this device — sign in to sync · how this works

0/600

Questions students ask

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

A letter (variable) lets us write a general rule or an unknown value in a short, clear way, so we can describe patterns and solve problems without knowing the exact number first.

Do the same operation on both sides to get the variable alone: subtract 5 from both sides to get x = 7.

Practice more, ask doubts, find a tutor

Tamil Nadu (TNBSE) Class 6 mock tests

Tamil Nadu (TNBSE) Class 6 PYQs

Ask in Q&A

Mathematics flashcards

Related chapters

Students who read Introduction to Algebra usually read these next.

Numbers (Term 1) - Whole Numbers

Samacheer Kalvi (TN State Board) Class 6 Maths — Term 1 Chapter 1, Numbers. Reading and writing large numbers, place value and the Indian and international systems, ascending and descending order, rounding (estimation), the properties of whole numbers and the BODMAS rule, with worked examples, exercises and quick revision.

Ratio and Proportion

Samacheer Kalvi (TN State Board) Class 6 Maths — Term 1 Chapter 3, Ratio and Proportion. The meaning of a ratio, equivalent ratios and simplest form, the meaning of proportion, and the unitary method for solving everyday problems, with worked examples, exercises and quick revision.

Geometry (Term 1) - Lines and Angles

Samacheer Kalvi (TN State Board) Class 6 Maths — Term 1 Chapter 4, Geometry. Points, lines, rays and line segments, measuring angles with a protractor, the types of angles, special angles (30°, 45°, 60°, 90°, 120°) and supplementary angles, with worked examples, exercises and quick revision.

Statistics (Term 1) - Data Handling

Samacheer Kalvi (TN State Board) Class 6 Maths — Term 1 Chapter 5, Statistics. Collecting and organising data, making a frequency table with tally marks, and representing data using pictographs and bar graphs, with worked examples, exercises and quick revision.

🧑‍🏫