Find Least Common Multiple of 4, 12, 20 and 24 using prime factorisation method.
Answer
LCM( 4, 12, 20, 24 ) = 120
Explanation
Step 1: Write down factorisation of each number:
4 = 2 · 2
12 = 2 · 2 · 3
20 = 2 · 2 · 5
24 = 2 · 2 · 2 · 3
Step 2 : Match primes vertically:
| 4 | = | 2 | · | 2 | ||||||
| 12 | = | 2 | · | 2 | · | 3 | ||||
| 20 | = | 2 | · | 2 | · | 5 | ||||
| 24 | = | 2 | · | 2 | · | 2 | · | 3 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 4 | = | 2 | · | 2 | ||||||||
| 12 | = | 2 | · | 2 | · | 3 | ||||||
| 20 | = | 2 | · | 2 | · | 5 | ||||||
| 24 | = | 2 | · | 2 | · | 2 | · | 3 | ||||
| LCM | = | 2 | · | 2 | · | 2 | · | 3 | · | 5 | = | 120 |
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