Addition and Subtraction

Solving Problems

In Lesson 1, you learned how to use counting to solve addition problems. That skill can also be used to solve subtraction problems.

For instance, can you use counting to solve this problem?

Ways to Count

 We're going to take a look at two ways you can use counting to subtract. First we'll count with objects.

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  To count with objects, use the objects to show the first number in the expression.

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  Let's try it with this expression, 9 - 4.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We'll start by showing the number 9. We'll need 9 objects.

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  We're subtracting 4, so we'll take away 4 of the objects.

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  We're subtracting 4, so we'll take away 4 of the objects.

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  We're subtracting 4, so we'll take away 4 of the objects.

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  We're subtracting 4, so we'll take away 4 of the objects.

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  We're subtracting 4, so we'll take away 4 of the objects.

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  Now we can finish this expression. All we have to do is count the remaining objects.

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  Now we can finish this expression. All we have to do is count the remaining objects.

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  Now we can finish this expression. All we have to do is count the remaining objects.

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  Now we can finish this expression. All we have to do is count the remaining objects.

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  Now we can finish this expression. All we have to do is count the remaining objects.

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  Now we can finish this expression. All we have to do is count the remaining objects.

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  There are 5 objects left, so our answer is 5.

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  To finish, we'll write 5 to the right of the equals sign.

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Now, try it! Solve these expressions. If you'd like, you can count. To count with beans, simply click the white bean and drag beans into the scratch space. To subtract beans, drag them out of the scratch space.

Number Lines

Another way to solve subtraction problems is to use a number line.

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  Subtracting with a number line is simple.

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  When you subtract, you count by moving left one number at a time.

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  When you subtract, you count by moving left one number at a time.

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  When you subtract, you count by moving left one number at a time.

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  Let's practice subtracting with a number line.

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  We need to start counting from the first number in our expression.

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  Here, that number is 9...

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  Here, that number is 9...So, we'll start counting at the 9 mark on the number line.

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  The second number in our expression is how much we're subtracting.

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  Here, that number is 4...

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  Here, that number is 4...So, we'll move to the left 4 times.

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  Here, that number is 4...So, we'll move to the left 4 times.

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  Here, that number is 4...So, we'll move to the left 4 times.

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  Here, that number is 4...So, we'll move to the left 4 times.

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  We landed on 5. This means that 9 - 4 = 5.

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  We'll write 5 to the right of the equals sign. Our expression is complete!

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