Question
Find Least Common Multiple of 18, 24, 30, 36 and 20 using ladder method..
Answer
LCM( 18, 24, 30, 36, 20 ) = 360
Explanation
Step 1 : Place the numbers inside division bar:
| 18 | 24 | 30 | 36 | 20 |
Step 2 : Find a prime number which can divide at least two of your numbers.
In this example we can divide by 2. If any number is not divisible by 2 write it down unchanged.
| 2 | 18 | 24 | 30 | 36 | 20 |
| 9 | 12 | 15 | 18 | 10 |
Step 3 : Repeat Step 2 until you can no longer divide.
| 2 | 18 | 24 | 30 | 36 | 20 |
| 2 | 9 | 12 | 15 | 18 | 10 |
| 9 | 6 | 15 | 9 | 5 |
| 2 | 18 | 24 | 30 | 36 | 20 |
| 2 | 9 | 12 | 15 | 18 | 10 |
| 3 | 9 | 6 | 15 | 9 | 5 |
| 3 | 2 | 5 | 3 | 5 |
| 2 | 18 | 24 | 30 | 36 | 20 |
| 2 | 9 | 12 | 15 | 18 | 10 |
| 3 | 9 | 6 | 15 | 9 | 5 |
| 3 | 3 | 2 | 5 | 3 | 5 |
| 1 | 2 | 5 | 1 | 5 |
| 2 | 18 | 24 | 30 | 36 | 20 |
| 2 | 9 | 12 | 15 | 18 | 10 |
| 3 | 9 | 6 | 15 | 9 | 5 |
| 3 | 3 | 2 | 5 | 3 | 5 |
| 5 | 1 | 2 | 5 | 1 | 5 |
| 1 | 2 | 1 | 1 | 1 |
Since there are no primes that divides at least two of given numbers, we conclude that the LCM is a product of starting numbers.
LCM = 18 · 24 · 30 · 36 · 20 = 360
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