Find Least Common Multiple of 20, 56 and 70 using prime factorisation method.
Answer
LCM( 20, 56, 70 ) = 280
Explanation
Step 1: Write down factorisation of each number:
20 = 2 · 2 · 5
56 = 2 · 2 · 2 · 7
70 = 2 · 5 · 7
Step 2 : Match primes vertically:
| 20 | = | 2 | · | 2 | · | 5 | ||||
| 56 | = | 2 | · | 2 | · | 2 | · | 7 | ||
| 70 | = | 2 | · | 5 | · | 7 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 20 | = | 2 | · | 2 | · | 5 | ||||||
| 56 | = | 2 | · | 2 | · | 2 | · | 7 | ||||
| 70 | = | 2 | · | 5 | · | 7 | ||||||
| LCM | = | 2 | · | 2 | · | 2 | · | 5 | · | 7 | = | 280 |
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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