LCM( 6, 7, 12, 21 ) = 84
Step 1: Write down factorisation of each number:
6 = 2 · 3
7 = 7
12 = 2 · 2 · 3
21 = 3 · 7
Step 2 : Match primes vertically:
6 | = | 2 | · | 3 | ||||
7 | = | 7 | ||||||
12 | = | 2 | · | 2 | · | 3 | ||
21 | = | 3 | · | 7 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
6 | = | 2 | · | 3 | ||||||
7 | = | 7 | ||||||||
12 | = | 2 | · | 2 | · | 3 | ||||
21 | = | 3 | · | 7 | ||||||
LCM | = | 2 | · | 2 | · | 3 | · | 7 | = | 84 |