GCF and LCM for Kids: Greatest Common Factor and Least Common Multiple (Grade 6 Math)

Hi, I'm Luna from DoodleBeez. Today we are finding the greatest common factor and the least common multiple. Factors divide into a number, and multiples are what you get when you count by a number.

The greatest common factor is the biggest number that divides into both numbers. List the factors of twelve and eighteen. They share one, two, three and six. The biggest one they share is six.

The least common multiple is the smallest number that both numbers divide into. Count by fours and by sixes. Twelve is the first number on both lists, so the least common multiple of four and six is twelve.

Prime factors work too. Twelve is two times two times three. Eighteen is two times three times three. Multiply the primes they share, two times three, to get the GCF of six. Use every prime the most times it appears for the LCM, thirty six.

The GCF helps us factor a sum. Thirty six plus eight: the greatest common factor is four. Pull the four out front. Thirty six plus eight equals four times the sum of nine and two.

Real problems need these ideas too. Juice boxes come in packs of six, and granola bars come in packs of eight. To buy the same number of each, find the LCM. The smallest number is twenty four.

Now it's your turn. Find the GCF and the LCM of eight and twelve. Pause and try. The biggest shared factor is four. The smallest shared multiple is twenty four.

Great job! Remember, the GCF is the biggest factor two numbers share, and the LCM is the smallest multiple they share. Lists or prime factors both work. Practice GCF and LCM in Middle School Math at doodlebeez.com. See you next time!