LCM( 6, 12, 18, 20 ) = 180
Step 1: Write down factorisation of each number:
6 = 2 · 3
12 = 2 · 2 · 3
18 = 2 · 3 · 3
20 = 2 · 2 · 5
Step 2 : Match primes vertically:
6 | = | 2 | · | 3 | ||||||
12 | = | 2 | · | 2 | · | 3 | ||||
18 | = | 2 | · | 3 | · | 3 | ||||
20 | = | 2 | · | 2 | · | 5 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
6 | = | 2 | · | 3 | ||||||||
12 | = | 2 | · | 2 | · | 3 | ||||||
18 | = | 2 | · | 3 | · | 3 | ||||||
20 | = | 2 | · | 2 | · | 5 | ||||||
LCM | = | 2 | · | 2 | · | 3 | · | 3 | · | 5 | = | 180 |