# Missing Numbers in Subtraction

Content Missing Numbers in Subtraction
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Missing Numbers in Subtraction
CCSS.MATH.CONTENT.2.OA.A.1

## Finding Missing Numbers in Subtraction

How do you find the missing number in subtraction? The answer depends on the missing numbers for subtraction in the number sentence. Sometimes instead of finding the difference, or answer, we have to find the number that is being subtracted:

Sometimes we have to find the number we started with.

When subtracting with missing numbers, there are two different ways to solve. In the next section, you will learn how to fill in subtraction missing numbers.

## Solving Subtraction with Missing Numbers

In the number sentence above, five minus blank equals three, we know five minus some number equals three.

In order to solve this problem, we can rewrite the number sentence by moving the number from after the equal sign to before the equal sign.

Now solve five minus three to get the answer, two. No matter what you are solving for, always check your answer using the original number sentence.

Next, the first number is missing in the number sentence.

We know that some number minus two equals three. In order to find the missing number, we can rewrite the equation as three plus two, to get the answer five. No matter what you are solving for, always check your answer using the original number sentence.

## Missing Numbers in Subtraction – Summary

How do you find the missing number in subtraction? The answer depends on the missing numbers for subtraction in the number sentence. Follow these steps to find the missing number in a subtraction problem.

Step # What to do
1 Find out which number is missing in the problem.
2 Rewrite the number sentence by moving the number
from after the equal sign to before the equal sign.
3 No matter what you are solving for, always check
your answer using the original number sentence.

Sometimes instead of finding the difference, or answer, we have to find the number that is being subtracted. No matter what you are solving for, always check your answer using the original number sentence.

Want to practice identifying missing numbers in subtraction? In this video you can find missing numbers in subtraction examples and on this website there is a missing numbers subtraction worksheet, missing numbers subtraction worksheets, along with other activities, and exercises.

## Missing Numbers in Subtraction exercise

Would you like to apply the knowledge you’ve learned? You can review and practice it with the tasks for the video Missing Numbers in Subtraction.
• ### How many bananas were eaten?

Hints

Remember, you can switch the number sentence around and subtract 15 from 32 to find the answer.

Use the image to help you, how many banana skins are there?

Solution

Someone has eaten 17 bananas.

To find the answer we can switch the number sentence around and solve 32 - 15 which equals 17.

• ### How many of each item has been eaten?

Hints

In this example, there were 25 cupcakes and Imani found 11 wrappers so we want to figure out the difference between 25 and 11. How could we solve this?

We would solve 25 - 11, which equals 14. There would be 14 cupcakes left in this example.

Subtract the number of items eaten from the amount that Imani started with to find the answer.

Solution
• 14 cupcakes had been eaten (36 - 14 = 22).
• 17 apples had been eaten (29 - 17 = 12).
• 24 ice-cream cones had been eaten (51 - 24 = 27).
• 34 chips had been eaten (67 - 34 = 33).
• ### Find the missing numbers.

Hints

If the first number is missing you can add the other two numbers to find the answer.

If the middle number is missing you can subtract the answer from the first number to find the missing number.

Always check your answers by performing the inverse operation.

You could use part part whole models like these to help you.

Solution

1.54 - 42 = 12

• To solve this we can add 42 + 12 = 54
2.68 - 38 = 30
• To solve this we can subtract 30 from 68: 68 - 30 = 38
3.75 - 53 = 22
• To solve this we can add 53 + 22 = 75
4.87 - 21 = 66
• To solve this we can add 21 + 66 = 87
5.49 - 32 = 17
• To solve this we can subtract 17 from 49: 49 - 17 = 32

• ### Which number is missing?

Hints

If the first number is missing, what should you do with the other two numbers?

If the middle number is missing, where can you move the final number?

Check your answers by performing the inverse.

For example, once you have worked out what you add to 21 to get 49 by solving 49 - 21 = ?, you can add 21 + ? to check it equals 49.

Solution

28

• 28 - 16 = 12
• 49 - 28 = 21
37
• 37 - 25 = 12
• 70 - 37 = 33
46
• 46 - 22 = 24
• 68 - 46 = 22
• 59 - 46 = 13

• ### How many screws have Mr. Squeaks and Imani used?

Hints

Where could you move the 16 to to help you solve this problem?

You could try using a part part whole model like this to help find the answer.

Try solving 48 - 16 to find the correct answer.

You can check your answer by adding it to 16. If it equals 48, then you have found the correct number.

Solution

Mr. Squeaks and Imani have used 32 screws. 48 - 32 = 16.

We can figure this out by solving 48 - 16 which equals 32. We can check our answer by adding 16 + 32 which equals 48.

• ### How much energy did Imani start with today?

Hints

The first number is missing in this subtraction problem, so what do you need to do with the other numbers to find the answer?

You are trying to solve ? - 28 - 13 - 31 = 18. What would the inverse of this be?

Solution

Imani started with 90 units of energy today.

90 - 28 - 13 - 31 = 18

We can solve this by adding 18 + 31 + 13 + 28 to get 90.