Question

Find the LCM of 12, 15 and 18 using prime factorisation method.

• A. 80
• B. 90
• C. 180
• D. 60

Answer 1

The correct option is C 180

Using prime factorisation,

$12=2\times 2\times 3$
$15=3\times 5$
$18=2\times 3\times 3$

The prime factors here are 2, 3, 5
The LCM of the two numbers is the product of the prime factors
counted the maximum number of times they occur in any of the numbers.

2 occurs twice, 3 occurs twice, 5 occurs once.

$LCM=2\times 2\times 3\times 3\times 5=4\times 9\times 5=180$

Therefore, LCM of 12, 15, 18 is 180.