NCERTCh 3Free

Finding Common

🎓 Class 7📖 Ganita Prakash-II📖 6 notes🧠 15 Q&A⏱️ ~9 min

Finding CommonStudy Notes

NCERT-aligned · 6 notes · 3 shown free

Introduction

Explanation

Introduction

The chapter 'Finding Common' introduces the concept of finding common multiples of numbers, which is a fundamental aspect of number theory and arithmetic. It begins by explaining the need to find a number that is common to two or more given numbers, especially when dealing with problems related to synchronization, scheduling, or grouping. The chapter emphasizes the importance of understanding multiples and common multiples to solve real-life problems efficiently. It also sets the stage for learning about the Least Common Multiple (LCM), which is the smallest number that is a multiple of two or more numbers. The introduction highlights how finding common multiples helps in comparing fractions, adding and subtracting fractions with different denominators, and solving problems involving repeated events occurring at different intervals.

  • Common multiples are numbers that are multiples of two or more numbers simultaneously.
  • Understanding common multiples is essential for solving problems involving synchronization and scheduling.
  • The concept of LCM helps find the smallest common multiple of given numbers.
  • Finding common multiples is useful in operations with fractions and in real-life applications.
  • The chapter lays the foundation for learning about LCM and its applications.
  • It connects number theory concepts with practical problem-solving.
  • 📌 Multiple: A number obtained by multiplying a given number by an integer.
  • 📌 Common Multiple: A number that is a multiple of two or more numbers.
  • 📌 Least Common Multiple (LCM): The smallest common multiple of two or more numbers.

Multiples and Common Multiples

Explanation

Multiples and Common Multiples

This section delves into the formal definition of multiples and common multiples. A multiple of a number is defined as the product of that number and any integer. For example, multiples of 3 are 3, 6, 9, 12, and so on. The section explains how to list multiples of given numbers and identify common multiples by comparing these lists. It emphasizes that common multiples are numbers that appear in the multiples list of each number considered. The section also discusses that there are infinitely many multiples and hence infinitely many common multiples for any two numbers, but among them, the smallest positive common multiple is of special interest. This smallest positive common multiple is called the Least Common Multiple (LCM). The section provides examples to illustrate these concepts and explains the significance of finding common multiples in solving practical problems such as scheduling events that occur at different intervals.

  • Multiple of a number is the product of the number and an integer.
  • Common multiples are numbers that appear in the multiples list of all given numbers.
  • There are infinitely many multiples and common multiples for any number(s).
  • The smallest positive common multiple is called the Least Common Multiple (LCM).
  • Listing multiples helps in identifying common multiples.
  • Common multiples are useful in solving problems involving repeated events.
  • 📌 Multiple: Number obtained by multiplying a given number by an integer.
  • 📌 Common Multiple: A number that is a multiple of two or more numbers.
  • 📌 Least Common Multiple (LCM): The smallest positive common multiple.

Finding the Least Common Multiple (LCM)

Explanation

Finding the Least Common Multiple (LCM)

This section introduces the concept of the Least Common Multiple (LCM) in detail. The LCM of two or more numbers is defined as the smallest positive number that is a multiple of all the numbers. The section explains why the LCM is important, especial

Practice QuestionsFinding Common

15 practice questions with detailed answers

Q1.Which of the following is a common multiple of 4 and 6?
A.A) 10
B.B) 12
C.C) 14
D.D) 18

Answer:

12

Explanation:

Multiples of 4 are 4, 8, 12, 16, 20, ... and multiples of 6 are 6, 12, 18, 24, ... The common multiples are numbers that appear in both lists. 12 is the smallest common multiple of 4 and 6.

Easy
Q2.Fill in the blank: A number that is a multiple of two or more numbers is called a _____ multiple.

Answer:

common

Explanation:

A common multiple is a number that is a multiple of two or more numbers. For example, 12 is a common multiple of 4 and 6 because it appears in the multiples of both numbers.

Easy
Q3.Why is the Least Common Multiple (LCM) important when adding fractions with different denominators?

Answer:

The Least Common Multiple (LCM) is important in adding fractions because it helps find the smallest common denominator. For example, to add 1/4 and 1/6, the LCM of 4 and 6 is 12, which is used as the common denominator to add the fractions easily.

Explanation:

The LCM provides a common base (denominator) to combine fractions with different denominators. This simplifies the addition or subtraction process and ensures accuracy.

Medium
Q4.List the first five multiples of 7.

Answer:

The first five multiples of 7 are 7, 14, 21, 28, and 35. Multiples of a number are found by multiplying the number by integers starting from 1.

Explanation:

Multiples of 7 are calculated by 7×1=7, 7×2=14, 7×3=21, 7×4=28, and 7×5=35. These are the first five multiples.

Easy
Q5.Explain the division method (ladder method) to find the LCM of numbers.

Answer:

The division method involves dividing the given numbers by common prime factors step-by-step until all the numbers become 1. The LCM is found by multiplying all the prime divisors used. For example, to find the LCM of 12 and 18, divide both by 2, then by 3, and multiply the divisors 2×3×2=12.

Explanation:

This method systematically reduces numbers by their prime factors and collects all prime divisors to find the smallest common multiple. It is efficient for larger numbers.

Medium
Q6.Which of the following is the Least Common Multiple (LCM) of 8 and 12?
A.A) 24
B.B) 36
C.C) 48
D.D) 60

Answer:

24

Explanation:

Multiples of 8 are 8, 16, 24, 32, ... and multiples of 12 are 12, 24, 36, 48, ... The smallest common multiple is 24, so LCM(8,12) = 24.

Easy
Q7.Find the LCM of 15 and 20 using prime factorization.

Answer:

60

Explanation:

Given: 15 and 20 Find: LCM of 15 and 20 Prime factorization: 15 = 3 × 5 20 = 2² × 5 Take highest powers of all primes: 2², 3¹, 5¹ Formula: LCM = 2² × 3 × 5 Solution: Step 1: 2² = 4 Step 2: 4 × 3 = 12 Step 3: 12 × 5 = 60 Answer: 60 Note: Common mistake is to multiply numbers directly without prime factorization.

Medium
Q8.True or False: The LCM of any two numbers is always greater than or equal to both numbers.
A.True
B.False

Answer:

True

Explanation:

The Least Common Multiple (LCM) of two numbers is the smallest positive number that is a multiple of both. Since it must be a multiple of each number, it cannot be smaller than either number.

Easy