Print these cards on cardstock, laminate and cut, and then have the students match the pairs face up. Have the students match every blue card with a red card. Students will have a great discussion about factors and multiples and prime and composite numbers while matching the cards. When they have matched the pairs, have the students make two separate arrays placing the cards face down this time while they play a game of memory, drawing one card from each array until they find all the matches.
My 4th graders LOVE playing this hands-on game which helps them practice their factors and multiples as well as review prime and composite numbers. I like to have my student play in partners, but groups of 3 also work well.