NCERT Ganita Manjari, Class 9, textbook pages 37–50 (Part II)

How to help your child with Class 9 Maths Chapter 11, The World of Algorithms, at home

Step-by-step procedures: addition, GCD, data structures, explained for parents: a 30-minute study session, a quick challenge, a 5-day plan and the mistakes to watch for.

GCD(252, 105)252 = 2 × 105 + 42 → 105 = 2 × 42 + 21→ 42 = 2 × 21 + 0: GCD 21

NCERT Class 9 Maths Chapter 11 The World of Algorithms: what it teaches

An algorithm is a precise step-by-step procedure. Your teen analyses familiar algorithms like column addition, learns Euclid’s algorithm for the greatest common divisor, and meets simple ways to organise data such as lists and stacks.

Why it matters later. Algorithmic thinking underlies computer science and problem solving in later classes.

See it: this chapter in pictures

1. line up digits2. add each column from right3. carry tens left
Precise steps anyone can follow.
GCD(48, 18)48 = 2 × 18 + 12, 18 = 1 × 12 + 612 = 2 × 6: GCD 6
Repeat until the remainder is 0.
card 1card 2card 3card 4last in,first outa stack
A stack: the top card comes off first.

You need

  • paper
  • playing cards or numbered slips

Tonight’s 30 minutes

  1. Write the steps of column addition as numbered instructions.
  2. Find GCD(252, 105) with Euclid’s algorithm: 252 = 2 × 105 + 42, 105 = 2 × 42 + 21, 42 = 2 × 21 → 21.
  3. Sort 8 numbered cards by a clear rule and count the steps.
  4. Use a stack of cards: last in, first out.

Words to use

  • algorithm
  • step
  • input
  • output
  • GCD
  • Euclid’s algorithm
  • data structure

Watch for

  • Vague steps like “work it out”. Each step must be exact enough for a machine to follow.
  • Stopping Euclid’s algorithm too early. Continue until the remainder is 0; the last divisor is the GCD.

What it sounds like at home

A short example of the conversation. Your words will differ; the questions are what matter.

You252 and 105: GCD by Euclid?

Your child42, then 21, remainder 0: GCD 21.

A game for this week: Robot instructions

  1. One player writes steps to draw a shape.
  2. The other follows them exactly, like a robot.
  3. Fix unclear steps.
  4. Swap roles.

A 5-day plan, 30 minutes a day

  1. Day 1Algorithm for addition.
  2. Day 2Euclid’s GCD.
  3. Day 3Sorting cards.
  4. Day 4Stacks and lists.
  5. Day 5Robot instructions.

Everyday moments to practise

  • Recipes.
  • GPS route finding.
  • Search engines.
  • Sorting files and contacts.

Quick check

Ask these at the end of the week. Tap to see the answer.

GCD(252, 105)?

21.

GCD(48, 18)?

6.

Stack order: which card comes out first?

The last one put in.

Ready for the next chapter when your child…

  • Writes precise algorithms.
  • Uses Euclid’s algorithm.
  • Explains simple data structures.

Activities, wording and illustrations are Mathify Kids’ own, following the topics of NCERT’s Ganita Manjari (Class 9). See the full Class 9 parent guide for every chapter.

Questions parents ask

What is an algorithm?

A finite set of exact steps that solves a problem.

Why is Euclid’s algorithm fast?

The numbers shrink quickly with each division.

Is this coding?

It is the thinking behind coding, done on paper.