In the last post I discussed Prime Factor Decomposition, using factor trees. I also use this method for Highest Common Factor (HCF) and Lowest Common Multiple (LCM). The difference is you need two different coloured pens and a Venn diagram:
Factorise your first number
Factorise your second number
Draw and label an empty Venn diagram in appropriate colours
Fill in the common factors
Fill in the rest
HCF: Multiply the overlapping area
LCM: Multiply everything
Review
This method is great for visual learners who want to see where the numbers come from. You can also quickly spot where they have made a mistake in a calculation.
Challenge
This method also works for three numbers – just use three colours and three circles!