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Addition and Subtraction (The Place-value System)


Plus / Addition

Adding two positive numbers to each other makes things larger. When adding decimal numbers to each other, you add the numbers with the same place value together.

Rule

Important Words and Formulas

TERM + TERM = SUM

We usually say add together instead of plus or addition.

Example 1

You need to add 3 and 6 together.

Since both numbers are in the ones place, you can add them together directly. That gives you

3 + 6 = 9

Example 2

You need to add 12 and 25 together.

You can think like this:

  • The number 12 has 1 in the tens place and 2 in the ones place.

  • The number 25 has 2 in the tens place and 5 in the ones place.

  • First, you add the numbers in the ones place together. That gives you

    2 + 5 = 7
  • Then you can add the numbers in the tens place together. That gives you

    1 + 2 = 3
  • You have 3 in the tens place and 7 in the ones place. That makes the answer 37, which means that

    12 + 25 = 37

Minus / Subtraction

Subtracting positive numbers from each other makes things smaller. When subtracing decimal numbers from each other, you subtract the numbers with the same place value from each other. We usually say to subtract from instead of subtraction.

Rule

Important Words and Formulas

TERM TERM = DIFFERENCE

Example 3

You need to subtract 6 from 9.

Since both numbers are in the ones place, you can subtract directly. That gives you

9 6 = 3

Example 4

You need to subtract 25 from 48.

In this case you can think like this:

  • The number 48 has 4 in the tens place and 8 in the ones place.

  • The number 25 has 2 in the tens place and 5 in the ones place.

  • First, you need to subtract the numbers in the ones place from each other. That gives you

    8 5 = 3
  • Then you can subtract the numbers in the tens place from each other, which gives you

    4 2 = 2
  • You now have 2 in the tens place and 3 in the ones place. That means the answer is

    48 25 = 23

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Subtraction with Help from the Number Line
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How to Add Using the Column Method