Properties Of HCF And LCM

Properties of HCF and LCM: For the better understanding of the concepts of LCM (Lowest Common Multiple) and HCF (Highest Common Factor), we need to recollect the terms multiples and factors. Let’s learn about LCM, HCF, and relation between HCF and LCM of natural numbers.

Learn in detail: Hcf And Lcm

Definition of LCM and HCF

Lowest Common Multiple (LCM):  The least or smallest common multiple of any two or more given natural numbers are termed as LCM. For example, LCM of 10, 15, and 20 is 60.

Highest Common Factor (HCF): The largest or greatest factor common to any two or more given natural numbers is termed as HCF of given numbers. Also known as GCD (Greatest Common Divisor). For example, HCF of 4, 6 and 8 is 2.

4 = 2 × 2

6 =3 × 2

8 = 4 × 2

Here, the highest common factor of 4, 6 and 8 is 2.

Both HCF and LCM of given numbers can be found by using two methods; they are division method and prime factorization.

List of HCF and LCM Properties

Property 1

The product of LCM and HCF of any two given natural numbers is equivalent to the product of the given numbers.

LCM × HCF = Product of the Numbers

Suppose A and B are two numbers, then.

LCM (A & B) × HCF (A & B) = A × B

Example: If 3 and 8 are two numbers.

LCM (3,8) = 24

HCF (3,8) = 1

LCM (3,8) x HCF (3,8) = 24 x 1 = 24

Also, 3 x 8 = 24

Hence, proved.

Note: This property is applicable for only two numbers.

Property 2

HCF of co-prime numbers is 1. Therefore, LCM of given co-prime numbers is equal to the product of the numbers.

LCM of Co-prime Numbers = Product Of The Numbers

Example: Let us take two coprime numbers, such as 21 and 22.

LCM of 21 and 22 = 462

Product of 21 and 22 = 462

LCM (21, 22) = 21 x 22

Property 3

H.C.F. and L.C.M. of Fractions:

LCM of fractions = \(\frac{LCM \: of\: numerators}{HCF \: of\: denominators}\)

HCF of fractions = \(\frac{HCF \: of\: numerators}{LCM \: of\: denominators}\)

Example: Let us take two fractions 4/9 and 6/21.

4 and 6 are the numerators & 9 and 12 are the denominators

LCM (4, 6) = 12

HCF (4, 6) = 2

LCM (9, 21) = 63

HCF (9, 21) = 3

Now as per the formula, we can write:

LCM (4/9, 6/21) = 12/3 = 4

HCF (4/9, 6/21) = 2/63

Property 4

HCF of any two or more numbers is never greater than any of the given numbers.

Example: HCF of 4 and 8 is 4

Here, one number is 4 itself and another number 8 is greater than HCF (4, 8), i.e.,4.

Property 5

LCM of any two or more numbers is never smaller than any of the given numbers.

Example: LCM of 4 and 8 is 8 which is not smaller to any of them.

Solved Problems

Example 1: Prove that: LCM (9 & 12) × HCF (9 & 12) = Product of 9 and 12

Solution:
9 = 3 × 3 = 3²
12 = 2 × 2 × 3 = 2² × 3
LCM of 9 and 12 = 2² × 3² = 4 × 9 = 36

HCF of 9 and 12 = 3

LCM (9 & 12) × HCF (9 & 12) = 36 × 3 = 108

Product of 9 and 12 = 9 × 12 = 108

Hence, LCM (9 & 12) × HCF (9 & 12) = 9 × 12 = 108. Proved.

Example 2: 8 and 9 are two co-prime numbers. Using these numbers verify, LCM of Co-prime Numbers = Product Of The Numbers.

Solution: LCM and HCF of 8 and 9:

8 = 2 × 2 × 2 = 2³

9 = 3 × 3 = 3²

LCM of 8 and 9 = 2³ × 3² = 8 × 9 = 72

HCF of 8 and 9 = 1

Product of 8 and 9 = 8 × 9 = 72

Hence, LCM of co-prime numbers = Product of the numbers. Therefore, verified.

Example 3: Find the HCF of \(\frac{12}{25}\)\(\frac{9}{10}\)\(\frac{18}{35}\)\(\frac{21}{40}\).

Solution: Solution:
12 = 2 × 2 × 3
9 = 3 × 3
18 = 2 × 3 × 3
21 = 3 × 7
HCF (12, 9, 18, 21) = 3
25 = 5 × 5
10 = 2 × 5
35 = 5 × 7
40 = 2 × 2 × 2 × 5
LCM(25, 10, 35, 40) = 5 × 5 × 2 × 2 × 2 × 7 = 1400
The required HCF = HCF(12, 9, 18, 21)/LCM(25, 10, 35, 40) = 3/1400

To solve more problems on HCF and LCM download BYJU’S – The Learning App from Google Play Store and watch interactive videos. Also, take free tests to practice for exams.

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3 Comments

  1. Talib maqbool mir

    Nice ….well byjus helped me to go through the whole maths in just few minutes

  2. byjus is a good app
    to learn fast and quick

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