There is a simple mathematical procedure for finding the GCF and LCM of two numbers using a Venn diagram. Use this free math activity to help your kids understand how a Venn diagram works, and then to teach them how to find the GCF and LCM of two numbers with a Venn diagram. ‘GCF and LCM with Venn Diagrams’ makes it clear to fifth graders what GCF and LCM are all about, and also serves as a visual representation of the relationship between the two numbers.