Adding and Subtracting Fractions with Different Denominators

This free math video was kind of an experiment to see if my 8-year-old could assimilate all the information she’d learned thus far about fractions into adding and subtracting fractions with unlike denominators. I DO NOT want to give her rules until she has internalized the concepts, and, actually, I would prefer that she come up with the rules on her own when at all possible. That is why you will not see me straight up telling her what steps to take. I ask her what she thinks she should do, I give her a hint or the first step, but I try hard not to jump ahead to a “formula” too quickly. Understanding math concepts means understanding for life. Memorizing algorithms means forgetting in 10 or 20 or 30 years and feeling dumb. I’d prefer my children to actually understand this stuff!

Adding and subtracting fractions with Cuisenaire Rods looks exactly the same as adding whole numbers with the rods. The difference is in what rod you are calling “one.” Knowing how to add, subtract, multiply and divide whole numbers with the Cuisenaire rods makes it easy for her to do the same with fractions.

Improper Fractions War

Here is a great way to practice comparing fractions with unlike denominators using the least (or lowest) common multiple method. Cuisenaire Rods help make it visually obvious what we are talking about.

Be aware, though, that this is not an activity for those who have just recently been introduced to Cuisenaire Rods or fractions. This should be done after much play/work with both first so that children understand what the rods stand for.

This game idea comes from the Let’s Play Math blog. Here is the specific post:

Least Common Denominator

In this free math video, you’ll watch my 6 and 8-year-old make the connection on their own that when you add fractions with different denominators, you need to find the least/lowest common multiple of the denominators. It is so amazing to me to see them figuring these things out on their own. I remember being confused about this stuff in school because it was just a bunch of rules to memorize without explanation of WHY. My kids understand the WHY and so they are able to come up with the rules on their own. AMAZING!