# 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.

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### Practice Question 2

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

### Practice Question 3

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

17 – 8 =

### 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 =

### 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..

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

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