Fractions can be a piece of cake – especially when you’re literally slicing and dicing cake. Well, ok, in Crazy 8s’ Piece of Cake the cakes were made of paper. We promise no one ate any of them. But the kids DID figure out how to rearrange quarters, eighths and twelfths to make new “wholes” with 2 or 3 flavors. There was no escaping without building a massive new understanding of fractions!
But they also built up a big appetite. So go ahead and do these fraction activities with REAL cake at home! Take any tasty symmetrical dessert – circular cake or pie, or rectangular tray of brownies – and try these challenges with your kid.
*By the way, you have our permission to do this before a meal. We call it “pre-sert.”
With "circle desserts"
- Invite your child to use a butter knife (or real knife for cutting if they’re ready) to score the top of the cake or pie to mark 4 equal pieces.
- Talk about the reasoning: Scoring a line through the middle makes halves, and then scoring across those cuts each half in half. A half times a half is a quarter – and we even write it that way: 1/2 x 1/2 = 1/4.
- Just as 2 x 3 means you grabbed the number 2 3 “times” to make a total, it’s the same with fractions. You have 1/2, and you want it only half a “time.”
- Now score the pie again into thirds, using one of the original lines to mark one of the thirds.
- Look at where the other 2 lines land, and the gap between them and the quarter lines. What fraction are these gaps? They are twelfths, because 1/4 + 1/12 = 1/3
- Party Fun Fact: Equations like that are called Egyptian fractions.
With "rectangle desserts"
- Cut a nice-sized brownie equal to 3 or 4 servings (e.g. a 6 x 6 square) and put it on a plate or mat.
- Cut across the brownie to make 3 equal rows. These are thirds.
- Now ask your child how he/she would share this among 4 people total. It’s cut wrong, right? Discuss easy ways to do this. One is to cut vertically into quarters, resulting in 12 little cubes with 3 cubes for each person. Discuss how this looks different from the quarters.
- You can cut another brownie and try cutting fourths, then sharing among 5 people – or any other combination!
Face-Off!
For a less messy, less caloric option, you can play Face-Off with your kids!
- You and your child each draw a colorful face on a grid, then cut each one into its equal pieces.
- Then you roll dice to switch pieces with each other to make funny mixed-up faces! Watch out, Picasso.
- On each roll, discuss what fraction of the pieces have switched – and what fraction haven’t. You’ll see that those two fractions have to add up to the whole, i.e. 1!
Click here to download printable instructions and grids.
