Question
Find Least Common Multiple of 7, 28, 14 and 35 using prime factorisation method.
Answer
LCM( 7, 28, 14, 35 ) = 140
Explanation
Step 1: Write down factorisation of each number:
7 = 7
28 = 2 · 2 · 7
14 = 2 · 7
35 = 5 · 7
Step 2 : Match primes vertically:
| 7 | = | 7 | ||||||
| 28 | = | 2 | · | 2 | · | 7 | ||
| 14 | = | 2 | · | 7 | ||||
| 35 | = | 5 | · | 7 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 7 | = | 7 | ||||||||
| 28 | = | 2 | · | 2 | · | 7 | ||||
| 14 | = | 2 | · | 7 | ||||||
| 35 | = | 5 | · | 7 | ||||||
| LCM | = | 2 | · | 2 | · | 5 | · | 7 | = | 140 |
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