Related Subtraction Facts

Overview

In this lesson, we are going to learn about related subtraction facts. There are three numbers in a family and they are related in some way.

The best way to understand this is by taking a look at a simple subtraction problem.

5 – 3 = 2

Notice that we have three numbers 5, 3, and 2 and the problem reads 5 – 3 = 2.
What the related subtraction fact tells us is that we can switch the numbers 3 and 2 to also make the equation true.

If we switch the numbers 3 and 2, we get 5 – 2 = 3 which is TRUE. We can apply this to any subtraction problem.

Take a look at the example below.

The subtraction problem shows two circles and one circle is being subtracted.
We can SUBTRACT to find the difference.
We can use the subtraction sentence 3 – 1 = ___ for help.
When we SUBTRACT 3 minus 1, we have 2 left.
We say: THREE minus ONE equals TWO.
We write it like this: 3 – 1 = 2

We can also use these same three numbers in our math fact: 3, 1, and 2 to make a RELATED  FACT.

This time our math fact will read:  3 – 2 = 1  because we subtracted 2 this time to get a difference of 1.

3 – 1 = 2  is related to  3 – 2 = 1

They include the same three numbers.

Let’s take a look at another example with numbers.
This time, we are subtracting the number 7 from the number 9.
The first number in the subtraction sentence is called the MINUEND.
The second number in the subtraction sentence is called the SUBTRAHEND.
This problem reads as  9 – 7 = 2.
When the SUBTRAHEND 7 is subtracted from the MINUEND  9, we get a DIFFERENCE of 2.
DIFFERENCE is used to describe the amount that is left.

These facts are related:

9 – 7 = 2

9 – 2 = 7

Related subtraction facts use the same three numbers.

Let’s take a look at these facts.

5 – 1 =

5 – 4 =

They are related and have the same minuend. We can find their differences. The differences are also subtrahends too.

5 – 1 = 4  and  5 – 4 = 1

Here is another example:

8 – 6 =

8 – 2 =

They are related and have the same minuend. We can find their differences. The differences are also subtrahends too.

8 – 6 = 2  and  8 – 2 = 6

Sometimes, you might come across a subtraction fact with a missing minuend. You can use related facts to help you solve. Let’s take a look at this pair of facts:

10 – 4 = __

10 – __ = 4

In the first math fact, our difference is missing. We can subtract 4 from 10 to get an answer of 6.
Our second fact is related. It will have the same three numbers as our first fact.
Therefore, 10 – 6 = 4.

Here is another example.

11 – 3 = __

11 – __ = 3

In the first math fact, our difference is missing. We can subtract 3 from 11 to get an answer of 8.
Our second fact is related. It will have the same three numbers as our first fact.
Therefore, 11 – 8 = 3.

We can also write related subtraction facts when we are given three numbers. Let’s look at this example:

5     8     3

We know that the sum in each subtraction fact, the first number must be the largest number. Which number is the largest: 5, 8, or 3?

The number 8 is the largest. Therefore, the other two numbers will be our subtrahends and difference.

8 – __ = __

8 – __ = __

Let’s create our related facts using the numbers 5, 8, and 3!

8 – 5 = 3

8 – 3 = 5

Let’s look at one more example:

13      7      6

We know that the sum in each subtraction fact, the minuend must be the largest number. Which number is the largest: 13, 7, or 6?

The number 13 is the largest.

13 – __ = __

13 – __ = __

Let’s create our related facts using the numbers 13, 7, and 6!

13 – 6 = 7

13 – 7 = 6

Practice Question 1

Let’s practice! Write the subtraction sentences and solve the problems below.

REVEAL THE ANSWER

Practice Question 2

Let’s try another! Write the subtraction sentences and solve the problems below.

REVEAL THE ANSWER

Practice Question 3

Take a look at the math sentence below. Write the related subtraction fact. Then solve.

17 – 8 =

REVEAL THE ANSWER

Practice Question 4

Let’s try another one. Take a look at the math sentence below. Write the related subtraction fact. Then solve.

13 – 4 =

REVEAL THE ANSWER

Practice Question 5

Let’s try one more problem!
Look at the groups below.
How many are there in all?
Write the related subtraction sentences and solve..

REVEAL THE ANSWER

Now you’re ready to take a quick quiz on subtraction related facts!