Question
Find Least Common Multiple of 7, 11, 21 and 22 using prime factorisation method.
Answer
LCM( 7, 11, 21, 22 ) = 462
Explanation
Step 1: Write down factorisation of each number:
7 = 7
11 = 11
21 = 3 · 7
22 = 2 · 11
Step 2 : Match primes vertically:
| 7 | = | 7 | ||||||
| 11 | = | 11 | ||||||
| 21 | = | 3 | · | 7 | ||||
| 22 | = | 2 | · | 11 |
Step 3 : Bring down numbers in each column and multiply to get LCM:
| 7 | = | 7 | ||||||||
| 11 | = | 11 | ||||||||
| 21 | = | 3 | · | 7 | ||||||
| 22 | = | 2 | · | 11 | ||||||
| LCM | = | 2 | · | 3 | · | 7 | · | 11 | = | 462 |
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