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Subtract by Adding

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Basics on the topic Subtract by Adding

How Do You Do Addition and Subtraction?

There are many ways we can do addition and subtraction such as counting on or backwards, using a number line or hundred square or using base ten blocks. But can you subtract by adding? Yes, you can! Let’s learn all about the think addition to subtract strategy.

How To Subtract By Adding

You may know that there are many strategies to help solve addition equations, but did you know that there are many to solve subtraction equations as well? One of those is the think addition strategy, also known as subtract using addition!

You may be wondering, how does addition help subtraction? Addition and subtraction are related, meaning that we can use what we know about one to help us with the other! When using addition to solve subtraction equations;

  • First: create the subtraction equation

  • Then: think of an addition fact to help you subtract. You can do this by looking at the subtraction equation!

  • Next: take the smaller number from the subtraction equation to create the new addition equation

  • Finally: count up from the smaller number to find the answer!

Think Addition to Subtract - Practice

What is the easiest way to add and subtract numbers? Take a look at the example below and use the think addition or subtract using addition strategy to solve!

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Remember to create a new addition equation, and to count up to find the answer. We can create thirty plus what equals forty-six as our new addition equation.

Thirty plus sixteen equals forty-six, which means that forty-six minus thirty also equals sixteen!

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Think Addition to Subtract - Summary

Today we learny all about think addition to subtract, which is when you subtract using addition. When using addition to subtract;

  • First: create the subtraction equation

  • Then: Use the smaller number to create the new addition equation

  • Next: Count up to solve

  • Finally: Your answer to the addition equation is also the answer to your subtraction equation!

Looking for extra practice? After this video check out the interactive exercises and a think addition to subtract worksheet.

Transcript Subtract by Adding

"Come on, Imani! We've got to practice for the race." Imani is helping Mr. Squeaks train for his upcoming race. He starts at the twenty-three marker and runs to the ten marker, but how far did he actually run? Mr. Squeaks and Imani can "subtract by adding" to find this out! There are many different strategies and tools to help with addition, and there are many for subtraction as well! But, did you know that one of the strategies to help with subtraction is to actually use addition? Some people use this strategy because they prefer adding to subtracting. When using addition to subtract, start with the subtraction equation. What is the subtraction equation here? It's twenty-three minus ten. Then, remake it as an addition equation by starting with the smaller number. Our addition equation is ten plus something equals twenty-three. Next, count up from the first number to the answer, twenty-three. You can use many tools or strategies to count up, let's use a hundred square here.
Ten plus what equals twenty-three?

Finally, the amount you count up is the answer to your subtraction equation. Ten plus thirteen equals twenty-three! That means twenty-three minus ten ALSO equals thirteen. Mr. Squeaks has been practicing A LOT! If he just sprinted from the thirty-eight marker to the twenty marker, how many markers did he run? We can subtract by adding to find out! First, set up the subtraction equation. Here it is thirty-eight minus twenty. Then, remake it as an addition equation by starting with the smaller number. That means our equation becomes twenty plus something equals thirty-eight. Next, count up from the first number to the answer, thirty-eight. Remember, there are many ways to solve addition equations, let's try place value this time. Twenty plus what is thirty-eight?

Finally, the amount you count on is the answer to your subtraction equation. Twenty plus eighteen equals thirty-eight. That means thirty-eight minus twenty ALSO equals eighteen. Mr. Squeaks is on his final practice sprint before his big race! If he ran from the forty-six marker to thirty, how far did he run? In order to subtract by adding, remember to set up the equation first. That means we need to solve forty-six minus thirty. Then, remake it as an addition equation by starting with the smaller number. Which is thirty plus something equals forty-six. Then, solve the addition equation using a strategy or tool that works for you, this time let's use a number line. Thirty plus what equals forty-six? Finally, the amount you count on is the answer to your subtraction equation. Thirty plus sixteen equals forty-six! So, forty-six minus thirty ALSO equals sixteen. Before we see Mr. Squeaks' race, let's review. When using addition to subtract, start by creating a subtraction equation. Then, remake it as an addition equation by starting with the smaller number. Next, solve the addition equation using a strategy or tool. Finally, the amount you count on is the answer to your subtraction equation. Now, let's see that race! "I don't know about this anymore, Imani."

"Woah! Now that's what I'm talking about, thanks Imani!"

Subtract by Adding exercise

Would you like to apply the knowledge you’ve learnt? You can review and practice it with the tasks for the video Subtract by Adding.
  • Solve 20 - 12 by adding.

    Hints

    The first step is to write out the original subtraction equation.

    Re-order the subtraction equation as an addition problem. Start with the smaller number.

    Solution

    Step one: Write out the original subtraction: 20 - 12.

    Step two: Rewrite the equation as an addition: 12 + ___ = 20.

    Step three: Solve the addition equation by counting up from 12 to 20.

    Step four: Fill in answer as: 12 + 8 = 20. Then switch this around to 20 - 12 = 8.

  • Subtract by adding.

    Hints

    In order to solve with addition, rephrase the subtraction equation as an addition problem, starting with the smaller number.

    Re-arranging a subtraction equation as an addition problem can make it easier to count up to the solution and solve the equation.

    Solution

    1) 10 - 2 = ?
    2) 2 + ? = 10
    3) 2 + 8 = 10

    A good technique to solve with addition can be to count up from 2 to 10. The difference is your answer!

  • Word problems to equations.

    Hints

    When making a subtraction equation, write the larger number first and subtract the smaller number next.

    If Mr. Squeaks begins at the 6 marker and runs until the 12 marker this problem would be written as 12 - 6 = ? to find how far he ran.

    Solution
    • Mr. Squeaks started at the 23 marker and ran to the 10 marker becomes 23 - 10 = ___
    • Mr. Squeaks started at the 30 marker and ran to the 18 marker becomes 30 - 18 = ___
    • Mr. Squeaks started at the 5 marker and ran to the 15 marker becomes 15 - 5 = ___
    • Mr. Squeaks started at the 10 marker and ran to the 50 marker becomes 50 - 10 = ___
  • Subtraction to addition.

    Hints

    When remaking an equation, the larger number in the subtraction equation will be the solution in the addition equation.

    In order to solve with addition, rephrase the subtraction equation as an addition problem.

    Solution

    When remaking an equation, the larger number in the subtraction equation will be the solution in the addition equation.

    • 10 - 4 can be re-written as 4 + ___ = 10. 10 - 4 = 6 and 4 + 6 = 10.
    • 18 - 6 can be re-written as 6 + ___ = 18. 18 - 6 = 12 and 6 + 12 = 18.
    • 10 - 6 can be re-written as 6 + ___ = 10. 10 - 6 = 4 and 6 + 4 = 10.
    • 5 - 5 can be re-written as 5 + ___ = 5. 5 - 5 = 0 and 5 + 0 =5.
    • 20 - 5 can be re-written as 5 + ___ = 20. 20 - 5 = 15 and 5 + 15 = 20.

  • Tools for adding when subtracting.

    Hints

    A hundreds chart can be a good way to see the numbers while you are counting.

    A number line allows you to count and add quickly with tens before you start adding ones.

    A place value chart will let you easily see how many tens and ones you still need to add to the total.

    There are three correct choices.

    Solution
    • A number line allows you to count and add quickly with tens before you start adding ones.
    • A hundreds chart can be a good way to see the numbers while you are counting.
    • A place value chart will let you easily see how many tens and ones you still need to add to the total.
  • Solving subtraction equations by adding.

    Hints

    In order to solve with addition, rephrase the subtraction equation as an addition problem.

    Re-arranging a subtraction equation as an addition problem can make it easier to count up to the solution and solve the equation. Remember to rewrite again as a subtraction equation as the last step.

    Solution

    When remaking an equation, the larger number in the subtraction equation will be the solution in the addition equation. Then fill in the rest of the numbers step by step.

    Problem 1
    1) 10 - 6 = ?
    2) 6 + ___ = 10
    3) 6 + 4 = 10
    4) 10 - 6 = 4

    Problem 2
    1) 16 - 14 = ?
    2) 14 + ___ = 16
    3) 14 + 2 = 16
    4) 16 - 14 = 2