Tuition Center Singapore Secondary Math Tuition – Lowest Common Multiple (LCM)

1.The smallest common multiple among the common multiples of two or more numbers is called the lowest common multiple (LCM) of the given numbers.

Example 1

Multiples of 8: 8, 16, 24, 32, 40, 48, …
Multiples of 12: 12, 24, 36, 48, 60, …

The LCM of 8 and 12 is 24.

2.Another method to find the LCM of two or more numbers is by using prime fractorisation

Example 2

Find the lowest common multiple of 24 and 90.

24 = 2³ x 3
90 = 2 x 3² x 5

LCM = 2³ x 3² x 5 = 360

3.We can also find the LCM of two or more numbers by repeatly dividing the numbers by their prime factors

Example 3

Find the lowest common multiple of 21, 63 and 105.

3)21, 63, 105
7)  7, 21,    35
   )  1,  3,       5

LCM = 3 x 7 x 3 x 5 = 315

The LCM of 28, 63 and 105 is 315.

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