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Add and subtract within 20: FAQ

Frequently asked questions about adding  and subtracting within 20.

How can we use place value blocks to help add and subtract?

We can use place value blocks to represent each number we want to add, and then combine them to find the total.
For example, if we want to add 12+6, we can start by drawing 12 blocks and then make a second group of place value blocks that has 6 blocks. After we put them together, we will see there are 18 blocks.
An image of one tens rod and two ones blocks in one color and six ones blocks in another color.
For subtraction, we can use the blocks to represent the larger number, and then take away the appropriate number of blocks to find the difference.
For example, to subtract 148, we can draw a set of blocks that has 14 place value blocks. Then we can take away 8 place value blocks from the 14 blocks. Now, there are 6 blocks lets.
An image of 14 place value blocks with 6 blocks crossed off.

How can we use ten frames to help add and subtract?

Ten frames can be helpful for adding and subtracting because they allow us to visually see the numbers we're working with. To add using ten frames, we can fill in the frames with the numbers we want to add.
For example, if we want to add 8 and 4, we could fill in eight squares on one ten frame and four squares on another ten frame. By combining the two frames, we can see that the sum is 12.
There are two ten frames separated by a plus sign. The first ten frame has 8 dots. The second ten frame has 4 dots.
To subtract using ten frames, we can fill in the frame with the larger number and then remove squares to represent the smaller number. For example, if we want to subtract 3 from 7, we would fill in seven squares on the ten frame and then remove three squares. This would leave us with four squares filled in, which represents the difference.
One ten frame with 7 dots and 3 of the 7 crossed out.

How can we use number lines to help add and subtract?

We can use the number line to visually represent the two numbers being added or subtracted. For example, to solve 7+9, we can mark both 7 and 9 on the number line. Then we can see that adding the two numbers together will result in a sum 16.
A number line beginning at 0 and ending at 20. An arrow from 0 to 7 has +7 above it. Another arrow from 7 to 16 has +9 above it.
To solve 124, mark 12 on the number line. Then we can subtract 4 to see that the jump ends at 8.
A number line beginning at 0 and ending at 20. A box is around the number 12. An arrow from 12 to 8 has -4 above it.

How can we use arrays to help us add?

We can use arrays to represent repeated addition! For example, an array of 5 rows and 3 columns can be thought of as adding 5 threes.
An array of pigs shows 5 rows and 3 columns.

Where do we use addition and subtraction in the real world?

We use addition and subtraction all the time! For example, we might use them when we're counting money, dividing up snacks, or measuring ingredients for a recipe.

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