Question
Find Least Common Multiple of 10, 5, 4 and 20 using prime factorisation method.
Answer
LCM( 10, 5, 4, 20 ) = 20
Explanation
Step 1: Write down factorisation of each number:
10 = 2 · 5
5 = 5
4 = 2 · 2
20 = 2 · 2 · 5
Step 2 : Match primes vertically:
| 10 | = | 2 | · | 5 | ||
| 5 | = | 5 | ||||
| 4 | = | 2 | · | 2 | ||
| 20 | = | 2 | · | 2 | · | 5 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 10 | = | 2 | · | 5 | ||||
| 5 | = | 5 | ||||||
| 4 | = | 2 | · | 2 | ||||
| 20 | = | 2 | · | 2 | · | 5 | ||
| LCM | = | 2 | · | 2 | · | 5 | = | 20 |
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