Find Least Common Multiple of 4, 5, 7 and 10 using prime factorisation method.
Answer
LCM( 4, 5, 7, 10 ) = 140
Explanation
Step 1: Write down factorisation of each number:
4 = 2 · 2
5 = 5
7 = 7
10 = 2 · 5
Step 2 : Match primes vertically:
| 4 | = | 2 | · | 2 | ||||
| 5 | = | 5 | ||||||
| 7 | = | 7 | ||||||
| 10 | = | 2 | · | 5 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 4 | = | 2 | · | 2 | ||||||
| 5 | = | 5 | ||||||||
| 7 | = | 7 | ||||||||
| 10 | = | 2 | · | 5 | ||||||
| LCM | = | 2 | · | 2 | · | 5 | · | 7 | = | 140 |
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