Last week I wrote about using pizza fractions to create an equivalent fractions table. Today we will move on to adding and subtracting fractions! Here is the set we purchased and that you’ll see in the pictures below:
There is no reason you can’t just make your own pizza fractions either – just color some circles and cut them in the right number of pieces! It is important that you are accurate in creating equal size pieces for the fractions, so they can be exchanged for other equivalent fractions through size comparisons alone.
Pizza fractions are a great way to give hands on practice adding and subtracting fractions. Students often find fraction work confusing at first; changing it to a visual exercise helps it make sense when they move to working on paper. Here’s how to do it:
Adding and subtracting with the same denominator:
Start by writing down a problem, then pulling out the related fractions pile – meaning, all the ones with the same denominator (bottom number if it’s been a while!) as your problem. Then, use the pieces to create the problem and solve it.
Here’s an example: 1/8 + 2/8 = ? and 3/8 – 2/8 = ? The pizzas below show the solutions to these 2 problems.
Adding and subtracting with a different denominator:
Here is where you use the equivalents chart you built in lesson one in this series. Look at the problem, set it up using the pizza pieces, and then go to the equivalents chart and find an equivalent that is in the row for all of your denominators.
For example: if our problem is 1/3 + 1/4 – we first need to get out a 1/3 and a 1/4 pizza piece and set up the problem. Next we go to the chart, and will find that both 1/3s and 1/4ths have an equivalent in the 1/12ths column.
Then, get out the appropriate equivalent pieces for the problem. In this example, we need to get out the 1/12th pieces. Once you have them, set the equivalent pieces on top of the original pizza problem. When the appropriate number of pieces is set up, you can solve the problem!
This picture shows what I’m talking about – we’ve placed 1/12 pieces on top of the 1/3 and 1/4 problem slices. Now that the equivalents are in place, we can count the pieces and solve the problem: 1/3 + 1/4 = 4/12 + 3/12 = 7/12!
Subtraction works the same way. Let’s change our problem to 1/3 – 1/4. Once we set up the equivalent pieces, we can see that this problem is equivalent to 4/12 – 3/12. When we set out 4/12 and then remove 3 of them, we see the answer of 1/12!
Next lesson will be mutiplying and dividing fractions with pizza!