NCERT Class 8 Mathematics Ganita Prakash Part-II: Chapter 6 — Algebra Play
This chapter, 'Algebra Play,' from NCERT's Class 8 Mathematics Ganita Prakash Part-II, introduces students to the fun and practical applications of algebra. It revisits the use of algebra to model situations and solve equations, emphasizing finding unknown values. The chapter explores 'Think of a Number' tricks, demonstrating how algebra can explain why these puzzles always yield a specific result. Students learn to represent the steps of a trick algebraically, like starting with 'x', doubling it to '2x', adding four to get '2x + 4', dividing by two to reach 'x + 2', and finally subtracting the original number to arrive at '2'. The text encourages students to modify these games to achieve different outcomes and create more complex tricks. It also introduces a date-guessing trick, showing how algebraic representation can decode the chosen date based on the given steps and the final numerical answer, making algebra an engaging tool for entertainment and problem-solving.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 8 |
| Subject | Mathematics |
| Book | Ganita Prakash Part-II |
| Chapter | Chapter 6 — Algebra Play |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 2 minutes |
| Word count | 358 |
Learning outcomes
- Understand how algebra can be used to explain number tricks and puzzles.
- Represent the steps of a 'Think of a Number' trick using algebraic expressions.
- Solve and verify algebraic equations derived from number tricks.
- Modify existing tricks or create new ones with predictable outcomes.
- Apply algebraic thinking to decode date-guessing puzzles.
Vocabulary
| Word | Meaning |
|---|---|
| Algebra | A branch of mathematics dealing with symbols and the rules for manipulating those symbols. |
| Model | To represent a situation or problem using mathematical concepts. |
| Equation | A statement that asserts the equality of two expressions. |
| Unknown | A variable or quantity whose value is not yet determined. |
| Letter-numbers | Variables or symbols used to represent numbers in algebra. |
| Trick | A puzzle or game that relies on a hidden mathematical principle. |
| Puzzle | A game, toy, or problem designed to test ingenuity or knowledge. |
| Predict | To say or estimate that a specified thing will happen in the future. |
| Expression | A combination of numbers, variables, and mathematical operations. |
| Variable | A symbol (usually a letter) that represents a quantity that can change. |
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Practice questions
- If you start with a number 'y', double it, add 6, divide by 2, and subtract the original number, what is the final result? Answer: 3
- How can you change the 'Think of a Number' trick (double it, add 4, divide by 2, subtract original number) to make the final answer 5? Answer: Change 'Add 4' to 'Add 10'.
- In the date trick, if the month is M and the day is D, what is the expression after multiplying the month by 5 and adding 6? Answer: 5M + 6
- If the result of the date trick is 291, and you know the steps were: Multiply month by 5, add 6, multiply by 4, add 9, add the day. Can you find the date? Answer: This requires reversing the steps, which is part of the chapter's exploration.
Frequently asked questions
What is the main goal of the 'Algebra Play' chapter?
The chapter aims to make learning algebra fun by exploring tricks and puzzles, and showing how algebra can explain why they work.
Can algebra be used to solve number tricks?
Yes, algebra is used to represent the steps of a number trick with variables, which helps in understanding and proving the consistent outcome.
What is an example of a 'Think of a Number' trick explained in the chapter?
A trick where you think of a number, double it, add four, divide by two, and subtract the original number, always resulting in 2.
How does the chapter explain why number tricks work?
By using algebraic expressions to represent each step of the trick, showing that the variable cancels out, leaving a constant result.
What is the date trick about?
It's a puzzle where specific mathematical operations are applied to a date (month and day), and a person can guess the date from the final number.
Can students create their own number tricks after reading this chapter?
Yes, the chapter encourages students to invent new tricks and puzzles using algebraic principles.
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NCERT Class 8 Mathematics — Ganita Prakash Part-II — Chapter 6 — Algebra Play. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.