# Subtract Using Addition on a Number Line

Content Subtract Using Addition on a Number Line
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## What do you learn about subtracting using addition?

When solving subtraction problems, you can us addition to subtract. There are many tools and strategies to solve addition problems, one of which is using a number line! When using addition to solve subtraction problems...

• Start by creating a new addition equation using what you know from the subtraction equation.

• Next, put the smaller addend on the left side of the number line.

• Then, count up using the bigger number in the equation. You can do this by counting forward small amounts, like by fives or tens!

• Finally, find your sum by looking at how much you counted to get to the second number. Remember, the answer to the addition equation is also the answer to your subtraction equation!

### TranscriptSubtract Using Addition on a Number Line

Mr. Squeaks and Imani are building a boat. However, Imani has brought him too many items! Mr. Squeaks needs to subtract from the items. He can solve subtractions by counting on to work out how many items will be left over. Addition and subtraction are inverse, they are opposite operations. That means that we can use addition to solve a subtraction question. Let's use addition to solve some subtraction equations. When we solve a subtraction by counting on, or using addition we need to start by creating an addition equation. Then we can fill in what we know. Imani has brought Mr. Squeaks bits of plastic to build the frame of the boat. Imani brought him twenty-six pieces in total, but he only needs fourteen pieces. We can take this equation and use the inverse to find how many pieces they would have left over. Start with the smaller number, here it is fourteen. Fourteen plus something equals twenty six. To find our missing value put the smaller number on the left side of the number line and the larger number on the right side of the number line. Then, count up in steps until we reach twenty six. Here we can jump five, then another five, then one,then another one until we reach twenty six. How much have we jumped altogether? We have jumped twelve. Fourteen plus twelve equals twenty six. We can rearrange this equation to show twenty six minus fourteen equals twelve. Next, Imani brought Mr. Squeaks scraps of fabric for a flag! They brought Mr. Squeaks forty-five scraps of fabric, but he only needs nineteen. How many scraps will he have left over? Start by using the inverse to rewrite the subtraction problem as an addition with a missing value. Nineteen plus something equals forty five. Begin with the smaller number, here it is nineteen. Count up using a number line. Remember to always put the smaller number on the left side of the number line. Next, we count forward in steps until we reach forty five! Ten, twenty, twenty five, twenty six! Finally, the amount we counted forward, twenty-six, is the answer! Nineteen plus twenty-six equals forty-five. That means that forty-five minus nineteen equals twenty-six. The last thing Imani brought Mr. Squeaks were some toothpicks to make into the steering wheel. If they brought sixty-three toothpicks and Mr. Squeaks only needed twenty-eight, how many will be left over? We can solve the subtraction by using the inverse and counting on using the number line. Start by rewriting the equation as an addition with a missing value. Next, use a number line to count forward between the two amounts. Always start by putting the smaller number on the left. Then, count forward in steps until we reach the larger number. Add up the steps to see how far we have jumped forward. Ten, twenty, thirty, five. We have jumped forward thirty five. So this is our answer. Twenty-eight plus thirty-five equals sixty-three. Or if we re-arrange our equation, sixty-three minus twenty-eight equals thirty-five. Before we see that magical trip, let's review. When solving subtractions by counting on using a number line, rewrite the equation as an addition with a missing value. Next, put the smaller number on the left side of the number line. Then, count up to the larger number. Finally, add up the jumps to see how much was counted on in total. This is the answer! Now, let's see that trip! "It's working, Imani! We did such a great job, but why do I feel like I'm missing something? "Wait, hang on, Imani?!”

## Subtract Using Addition on a Number Line exercise

Would you like to apply the knowledge you’ve learnt? You can review and practice it with the tasks for the video Subtract Using Addition on a Number Line.
• ### Using addition to solve a subtraction.

Hints

Start by putting the smaller number first in the addition equation.

The larger number goes after the equals sign.

Solution

We have three parts to the equation. The smaller number is first and the blank is for the missing number. The larger number goes after the equals sign.

If we start on 6 and count up 8, we reach 14. So 14 - 6 = 8.

• ### How many boxes can they take?

Hints

The larger number is the total number of boxes.

The smaller number is the amount of boxes that can fit.

Count forward from 14 until you reach 32.

Solution

They have 32 boxes.

Only 14 can fit.

Write the equation 14 + 18 = 32.

They should remove 18 boxes from the boat.

• ### Inverse addition and subtraction equations.

Hints

When converting a subtraction equation to addition, place the smaller value first.

Place the larger value after the = sign.

Try solving the first question: 30 - 12. 30 - 12 = 8. What addition equation could use the three numbers: 12, 8 and 30?

Solution

When converting a subtraction equation to addition, place the smaller value first and the larger value after the = sign.

• 30 - 12 = 18 and 12 + 18 = 30
• 20 - 8 = 12 and 8 + 12 = 20
• 16 - 4 = 12 and 4 + 12 = 16
• 24 - 16 = 8 and 16 + 8 = 24
• ### Help Imani and Mr. Squeaks with their hopscotch game.

Hints

When going forward on the number line, start with the smaller number and count up to the larger number.

Mr. Squeaks jumps back 4 spots to reach 8. What number did he begin at?

When going backwards on the number line, start with the larger number and count back to reach the smaller number.

Solution
• Imani begins at 2 and jumps 7 spots to reach 9.
• Mr. Squeaks begins at 12 and goes back 4 spots to reach 8.
• Imani begins at 18 and goes back 12 spots to reach 6.
• Mr. Squeaks begins at 9 and jumps 10 spots to reach 19.
• ### Count up using the number line.

Hints

Begin at 6 and count up until you reach 10.

Count the jumps.

Solution

Begin with the smaller number 6 and count forward 4 to reach 10.

• ### Which friends can go?

Hints

First, calculate how many pounds you have left in the spaceship.

Add the different weights of the animals. Begin with the smaller numbers so the maximum number of friends can go.

Keep adding friends until you reach the weight allowance on the spaceship.

Solution

• Mr. Squeaks and Imani weigh 12 pounds in total.
• The total weight allowance in the spacship is 30 pounds.
• Therefore, we need to calculate 30 - 12 to find the allowance left.
• To solve 30 - 12, we can add. Start at 12, and count up until you reach 30. We count up 18.
• Next, we need to add as many friends as we can that total 18 pounds.
• Begin with the smallest number.
• 3 (frog) + 4 (duck) + 5 (tortoise) + 6 (dog) = 18.
The frog, duck, tortoise and dog can go on the spaceship, the elephant and bear must stay.