Find Least Common Multiple of 15, 20 and 40 using prime factorisation method.
Answer
LCM( 15, 20, 40 ) = 120
Explanation
Step 1: Write down factorisation of each number:
15 = 3 · 5
20 = 2 · 2 · 5
40 = 2 · 2 · 2 · 5
Step 2 : Match primes vertically:
| 15 | = | 3 | · | 5 | ||||||
| 20 | = | 2 | · | 2 | · | 5 | ||||
| 40 | = | 2 | · | 2 | · | 2 | · | 5 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 15 | = | 3 | · | 5 | ||||||||
| 20 | = | 2 | · | 2 | · | 5 | ||||||
| 40 | = | 2 | · | 2 | · | 2 | · | 5 | ||||
| LCM | = | 2 | · | 2 | · | 2 | · | 3 | · | 5 | = | 120 |
This solution can be visualized using a Venn diagram.
The LCM is equal to the product of all the numbers on the diagram.
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