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Tis simple!!

TO solve HCF:
Write down all the factors of the given numbers. Cross out repeating numbers. Find the biggest crossed number. That is the HCF.

TO solve LCM:
Write all the multiples of given numbers. Cross repeaters.Find the smallest of them. That is the LCM.

To find HCF take the common factors of given number and it is HCF
What about LCM?
And what you've just said isn't quite right. What if there are three or four common factors?