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Missing Numbers in Subtraction—Let's Practise!

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Basics on the topic Missing Numbers in Subtraction—Let's Practise!

Missing Numbers in Subtraction – Introduction

Get ready because today we're going to practise missing numbers in subtraction. It’s a great way to understand subtraction better by finding the missing number in a number sentence. Ready to begin? Let's go!

What Does it Mean to Find Missing Numbers in Subtraction?

Finding the missing number in subtraction means working out which number is missing from the subtraction equation to make it true.

For example, if you have the equation 15 - ? = 8, you can find the missing number by solving 15 - 8. Let’s practise this with some fun problems!

What does finding the missing number in subtraction mean?
How can you find the missing number in the equation 15 - ? = 8?
Why do we use this method?

Missing Numbers in Subtraction – Example

Let's solve a problem by finding the missing number in subtraction:

Problem

15 - ? = 8

Solution

Follow these simple steps to find the solution.

Step Explanation Result
Rewrite the number sentence Move 8 before the equals sign 15 - 8 = ?
Solve the new equation 15 - 8 7
Check your answer Put 7 in the original equation 15 - 7 = 8

So, 15 minus 7 equals 8!

Missing Numbers in Subtraction – Guided Practice

Let's try another problem together.

Problem

20 - ? = 12

How do you rewrite the number sentence?
How do you solve the new equation?
How do you check your answer?

So, 20 minus 8 equals 12!

Missing Numbers in Subtraction – Application

Now, try solving this problem on your own:

Problem ? - 5 = 9

How do you rewrite the number sentence?
How do you solve the new equation?
How do you check your answer?

So, 14 minus 5 equals 9!

Missing Numbers in Subtraction – Examples

To help yourself become fluent in finding missing numbers in subtraction, take a look at some more examples and complete them by following the steps.

Problem Rewrite the Equation Solve the Equation Check Your Answer Solution
18 - ? = 9 18 - 9 = ? 18 - 9 = 9 18 - 9 = 9 9
14 - ? = 7 14 - 7 = ? 14 - 7 = 7 14 - 7 = 7 7
? - 4 = 6 4 + 6 = ? 4 + 6 = 10 10 - 4 = 6 10
? - 3 = 5 3 + 5 = ? 3 + 5 = 8 8 - 3 = 5 8

Missing Numbers in Subtraction – Summary

Key Learnings from this Text:

  • Finding the missing number in subtraction helps us understand subtraction better by completing the number sentence.
  • Rewrite the equation to make solving easier.
  • Solve the new equation to find the missing number.
  • Check your answer by substituting it back into the original equation.

Keep practising finding missing numbers in subtraction to become a maths whiz! Check out more fun maths problems and activities on our website, such as subtraction using a number line, subtraction by counting on or using place value to subtract. Feel free to apply your skills and knowledge of subtraction and apply that to problem-solving with subtraction.

Missing Numbers in Subtraction – Frequently Asked Questions

What is finding the missing number in subtraction?
How do you represent a missing number in a subtraction problem?
Why is this method helpful?
Can you give an example of finding the missing number in subtraction?
What do you do after rewriting the equation?
How do you find the solution after solving the new equation?
Is this method only used for subtraction?
What should you remember when finding missing numbers in subtraction?
Where can I practise more problems like this?

Missing Numbers in Subtraction—Let's Practise! exercise

Would you like to apply the knowledge you’ve learnt? You can review and practice it with the tasks for the video Missing Numbers in Subtraction—Let's Practise!.

  • What's the missing number?
    Hints

    To rewrite the equation, swap 32 with the missing number.

    To find the missing number, solve 45 - 32.

    Solution

    45 - ? = 32

    45 - 32 = ?

    45 - 32 = 13. 13 is the missing number.

    Check your work. Put 13 back into the original equation. 45 - 13 = 32.

  • Find the missing number.
    Hints

    Rewrite the equation.

    • Swap the missing number with 16.
    • When the missing number is first in the original equation, change the operation sign to +.

    Solve the new equation

    • What is 16 + 21?
    • Put the answer into the original equation to check your work.
    Solution

    The missing number is 37.

    • Rewrite the equation as 16 + 21 = ?
    • Solve the new equation by adding 16 + 21 = 37.
    • Check your work. Put the missing number, 37, into the original equation. 37 - 21 = 16.

  • Find the missing numbers.
    Hints

    Step 1: Rewrite the equation.

    Swap the missing number with the number to the right of the equals sign.

    So, 46 - ? = 16 should be rewritten as 46 - 16 = ?

    Step 2: Solve the new equation. What is 46 - 16?

    The image below shows 46 blue dots. 16 are inside a red box.

    Count the number of blue dots outside of the red box to solve the equation.

    Step 3: Check your work.

    When you've found the answer, put it into the original equation: 46 - ? = 16.

    If you subtract the correct number from 46, you will get 16!

    Solution

    1. 46 - 30 = 16. The missing number is 30.
    • Rewrite the equation as 46 - 16 = ?
    • Subtract. 46 - 16 = 30.
    2. 59 - 26 = 33. The missing number is 26.
    • Rewrite the equation as 59 - 33 = ?
    • Subtract. 59 - 33 = 26.
    3. 80 - 11 = 69. The missing number is 11.
    • Rewrite the equation as 80 - 69 = ?
    • Subtract. 80 - 69 = 11.

  • Find all of the missing numbers.
    Hints

    Step one: rewrite the equation.

    Rewrite the equation so that the missing number is on the right of the equals sign.

    In this problem, the missing number is first in the original equation. This is shown by the red box in the image below.

    • When the missing number is first, make sure to rewrite your equation with a +.
    • The rewritten equation will be 12 + 45 = ?

    In this problem, the missing number is second.

    • When the missing number is second, do not change the operation sign.
    • Swap the numbers as shown in the image. The new equation will be 78 - 15 = ?
    Solution

    ? - 45 = 12. The missing number is 57.

    • Rewrite the equation as 12 + 45 = ?
    • Add 12 + 45 = 57.
    • Check your work. Put 57 into the original equation. 57 - 45 = 12
    ? - 43 = 9. The missing number is 52.
    • Rewrite the equation as 43 + 9 = ?
    • Add 43 + 9 = 52.
    • Check your work. Put 52 into the original equation. 52 - 43 = 9
    78 - ? = 15. The missing number is 63.
    • Rewrite the equation as 78 - 15 = ?
    • Subtract 78 - 15 = 63.
    • Check your work. Put 63 into the original equation. 78 - 63 = 15
    ? - 67 = 18. The missing number is 85.
    • Rewrite the equation as 67 + 18 = ?
    • Add 67 + 18 = 85.
    • Check your work. Put 85 into the original equation. 85 - 67 = 18

  • What's the missing number?
    Hints

    First, rewrite the equation so that the missing number is on the right of the = . This is done for you in the image.

    Solve the new equation: 51 - 37 = ?

    What is 51 - 37?

    This image shows 51 blue dots. 37 dots are in the red box.

    Count the number of dots outside of the red box to find 51 - 37.

    Solution

    51 - 37 = 14

    Put 14 into the original equation to check your work:

    51 - 14 = 37.

  • Solve the word problem.
    Hints

    We can write this problem as a subtraction equation.

    The number of sweets Razzi started with (70) - the sweets Razzi ate (?) = the number of sweets Razzi has left (49).

    Next, rewrite the equation so that the missing number is on the right of the equals sign.

    Solve the rewritten equation. The answer tells you how many sweets Razzi ate!

    Plug it back into the original equation to check your work.

    Solution

    Razzi ate 21 sweets.

    Step 1: Write the original equation

    • The original equation should be written as 70 - ? = 49.
    Step 2: Rewrite the equation
    • Rewrite the equation as 70 - 49 = ?
    Step 3: Solve the new equation
    • 70 - 49 = 21.
    Step 4: Check your work
    • Put 21 into the original equation. 70 - 21 = 49

More videos in this topic Subtraction problems
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Missing Numbers in Subtraction—Let's Practise!
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