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Session 31: The Least Common Multiple (LCM)

Session Title

The Multiple Mysteries 

Objective

By the end of this session, students will be able to:


1. Understand the concept of the Least Common Multiple (LCM)



2. Find the LCM of the given numbers using different methods.



3. Develop problem-solving and teamwork skills 

Topics

The Least Common Multiple (LCM) is the smallest multiple that two or more numbers share.


It is useful in real-life applications, such as scheduling events, solving fraction problems, and understanding patterns.

Material Required

Board & Chalk 

Before starting the class, draw a number grid ( up to 50 ) on the floor

Methodology

Activity-based Learning: Physical activity and group work.


Experiential Learning: Relating LCM to real-life situations.

Session Duration 

 90 Minutes

Introduction Activity 

GAME TIME

Pass pass - (10 Minutes)


In "Pass Pass," children form a circle. A target number is chosen. Starting with the first child, they count aloud in sequence. When a child's count reaches a multiple of the target number, they say "Pass" instead of the number. The next child continues the count. The game continues until only one child remains.(NB: Change the number after each round)


Main Topic/ Activity


Objective: Help students relate LCM to everyday life.


Tell a short story:- ( 20 minutes )


Two friends, Arya and Rahul, love visiting a park. Arya visits every 3 days, and Rahul visits every 4 days. If both visit the park today, when will they meet again?


Ask students to think and predict: “Will they meet again in a week? In 10 days?”


Guide them to count the days until both are at the park together (on the 12th day).


Explnumbers at the Least Common Multiple (LCM) of 3 and 4 is 12—the smallest number that both 3 and 4 can divide into evenly.



DEMO TIME  ( 30 minutes )


1. Draw a number grid on the floor (1–50)


2. Call out two numbers (e.g., 4 and 6)


3. Students take turns hopping on the multiples (4, 8, 12… and 6, 12, 18…)


4. The first common number they step on is the LCM 

 ( NB: Repeat the activity with different number )


TIME TO SOLVE: ( 20 Minutes)


Give simple examples: ( Devide students into small groups)


  • LCM of 2 and 5 

→ Multiples: (2, 4, 6, 8, 10, 12…) and (5, 10, 15…) → LCM is 10.


  • LCM of 6 and 8

→ Multiples: (6, 12, 18, 24…) and (8, 16, 24…) → LCM is 24.


  • A bell rings every 6 minutes, and another bell rings every 8 minutes. After how many minutes will both bells ring together?


  • A school organizes a sports day every 5 years, and a cultural fest every 7 years. How many years later will both events happen together again?


Expected Learning  Outcome:


Knowledge building-

  • Concept of LCM

  • Method to find LCM


Skill Building-

  • Logical thinking

  • Strengthens speed and accuracy

  • Team work 


Review Questions/Assessment/Tasks 


Ask: What strategies helped you solve the problems quickly?


Encourage peer teaching—students explain their solutions to classmates.


Follow up Task


Home work: ( 10 minutes)

1.Two farmers plant crops—one plants every 9 days, and the other every 12 days. In how many days will they plant on the same day again?


2.Two buses leave a station at the same time—one after 12 minutes, the other after 15 minutes. When will they leave together again?

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