Question
Find Least Common Multiple of 3, 7, 5, 3 and 8 using prime factorisation method.
Answer
LCM( 3, 7, 5, 3, 8 ) = 840
Explanation
Step 1: Write down factorisation of each number:
3 = 3
7 = 7
5 = 5
3 = 3
8 = 2 · 2 · 2
Step 2 : Match primes vertically:
| 3 | = | 3 | ||||||||||
| 7 | = | 7 | ||||||||||
| 5 | = | 5 | ||||||||||
| 8 | = | 2 | · | 2 | · | 2 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 3 | = | 3 | ||||||||||||
| 7 | = | 7 | ||||||||||||
| 5 | = | 5 | ||||||||||||
| 8 | = | 2 | · | 2 | · | 2 | ||||||||
| LCM | = | 2 | · | 2 | · | 2 | · | 3 | · | 5 | · | 7 | = | 840 |
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