LCM( 20, 60, 120, 140 ) = 840
Step 1: Write down factorisation of each number:
20 = 2 · 2 · 5
60 = 2 · 2 · 3 · 5
120 = 2 · 2 · 2 · 3 · 5
140 = 2 · 2 · 5 · 7
Step 2 : Match primes vertically:
20 | = | 2 | · | 2 | · | 5 | ||||||
60 | = | 2 | · | 2 | · | 3 | · | 5 | ||||
120 | = | 2 | · | 2 | · | 2 | · | 3 | · | 5 | ||
140 | = | 2 | · | 2 | · | 5 | · | 7 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
20 | = | 2 | · | 2 | · | 5 | ||||||||
60 | = | 2 | · | 2 | · | 3 | · | 5 | ||||||
120 | = | 2 | · | 2 | · | 2 | · | 3 | · | 5 | ||||
140 | = | 2 | · | 2 | · | 5 | · | 7 | ||||||
LCM | = | 2 | · | 2 | · | 2 | · | 3 | · | 5 | · | 7 | = | 840 |