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Question

Find Least Common Multiple of 100, 60, 80 and 120 using prime factorisation method.

Answer

LCM( 100, 60, 80, 120 ) = 1200

Explanation

Step 1: Write down factorisation of each number:

100 = 2 · 2 · 5 · 5

60 = 2 · 2 · 3 · 5

80 = 2 · 2 · 2 · 2 · 5

120 = 2 · 2 · 2 · 3 · 5

Step 2 : Match primes vertically:

100=2·2·      5·5
60=2·2·    3·5  
80=2·2·2·2·  5  
120=2·2·2·  3·5  

Step 3 : Bring down numbers in each column and multiply to get LCM:

100=2·2·      5·5  
60=2·2·    3·5    
80=2·2·2·2·  5    
120=2·2·2·  3·5    
LCM=2·2·2·2·3·5·5=1200
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