### Guide 5 - Adding and subtracting fractions

Students learn by example. Fractions Lab will show how two fractions can be added or subtracted. Learn how to add and subtract fractions and why it only works when the denominators are the same.

There are two ways to find the solution to an addition or subtraction problem. The first is to 'work out the answer in your head' then make the solution using the representation tool and trying it out in the addition and subtract box yourself.

Alternatively, Fractions Lab will find the solution for you.

### Adding and subtracting two fractions with like denominators

1. Make two fractions out of the same representation (Fractions Lab will not add different representations). E.g.:

2. Double click on the coloured part of each fraction. It will 'pop out' the numerator (coloured part):

3. Drag one of the coloured parts on top of the other, then left mouse click. An add/subtract menu will appear:

4. Select the operation you would like to use. An animation will appear showing the two coloured parts being joined or taken away.

### Have a go!

• Make two fractions with the same denominator and add them together
• Make two fractions with the same denominator and subtract them

• ### Adding and subtracting two fractions with unlike denominators

Have you seen your own students make the error 1/5 + 2/5 = 3/10?

In order to challenge students' misconceptions related to whole-number bias (adding the numerators and the denominators as if they were whole numbers), the Fractions Lab animation will not complete the addition or subtraction of fractions with different denominators.

This is an intentional design decision to encourage learners to consider the importance of making the fractions share the same denominator before they are operated upon.

### Have a go!

• Make two fractions with different denominators and add them together.
• Make two fractions with different denominators and subtract them.
• Once you have done these, change one or both of the fractions (perhaps using the 'Find equivalent' in the menu) so they have like denominators and try to add them again.
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