Find Least Common Multiple of 42, 60, 84 and 108 using prime factorisation method.
Answer
LCM( 42, 60, 84, 108 ) = 3780
Explanation
Step 1: Write down factorisation of each number:
42 = 2 · 3 · 7
60 = 2 · 2 · 3 · 5
84 = 2 · 2 · 3 · 7
108 = 2 · 2 · 3 · 3 · 3
Step 2 : Match primes vertically:
| 42 | = | 2 | · | 3 | · | 7 | ||||||||
| 60 | = | 2 | · | 2 | · | 3 | · | 5 | ||||||
| 84 | = | 2 | · | 2 | · | 3 | · | 7 | ||||||
| 108 | = | 2 | · | 2 | · | 3 | · | 3 | · | 3 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 42 | = | 2 | · | 3 | · | 7 | ||||||||||
| 60 | = | 2 | · | 2 | · | 3 | · | 5 | ||||||||
| 84 | = | 2 | · | 2 | · | 3 | · | 7 | ||||||||
| 108 | = | 2 | · | 2 | · | 3 | · | 3 | · | 3 | ||||||
| LCM | = | 2 | · | 2 | · | 3 | · | 3 | · | 3 | · | 5 | · | 7 | = | 3780 |
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