How do you subtract with fractions or mixed numbers by decomposing?

3 - = 3 - 1 2 -

In this lesson you will learn how to subtract with

fractions or mixed numbers by decomposing.

Let’s Review

We know that equivalent fractions show equal amounts.

= = = = =

This could go on forever!

How do I decide which equivalent fraction to use?

Let’s Review

Whole numbers can be decomposed as fractions or mixed numbers.

=

= =

The possibilities are endless!

1 22=

1 2 1 33

4 =5 4 =33

Let’s Review

Mixed numbers like 1 can be decomposed into their individual parts.

1

= +

A Common MisunderstandingForgetting to decompose.

≠

4 - 1 = 24 - 1≠ 3

Core Lesson

Think about cookies.

I need to subtract

Mom says I can eat the cookies if I give my sister

of a cookie.

I’ll cut just one cookie making two halves.

I don’t want to cut all the cookies.

Now I have 2 + I can easily subtract .

3 = 2

2 cookies

-

Core Lesson

This works with a fraction bar model.

3

2

- 12

12

11

= 2

=-

Core Lesson

This works with mixed numbers.

2

1

- =

= -

14

1414

14 I need to take

away one half, but the

minuend isn’t divided in

halves.

I will use an equivalent fraction.

=

I need to subtract from 2

I need to decompose into more pieces.

I will decompose one of the wholes

into .

When one denominator is a

divisor of the other, only one fraction

has to be changed.

= 1 + + = 2= 1

= 1

14

= 1

Core Lesson 3 - 1

3- 1

I need to subtract 1

I need to decompose one of the wholes

into .

= 2

= - 1 13

1

1

13

13

1

In this lesson you have learned

how to subtract with fractions or mixed numbers

by decomposing.