Addition (+) and subtraction (-) are inverse operations.

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This means that every addition is a subtraction in reverse, and every subtraction is an addition in reverse.

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3 + 2 = 5

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5 - 2 = 3

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Notice how the same three numbers are used, but in the reverse order. This fact is very useful for checking your answer when calculating.

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For example, you may perform the following subtraction:

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584 - 408 = 176 

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To check that this is correct you can reverse the subtraction into an addition (which most people find easier than subtraction):

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176 + 408 = 584

 

If you end up with the same three numbers, but in reverse order, you can be confident your subtraction was correct. 

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Multiplication (×) and division (÷) are inverse operations.

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This means that every multiplication is a division in reverse, and every division is a multiplication in reverse.

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5 × 2 = 10

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10 ÷ 2 = 5

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Notice how the same three numbers are used, but in the reverse order. This fact is very useful for checking your answer when calculating.

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For example, you may perform the following division:

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255 ÷ 3 = 85 

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To check that this is correct you can reverse the division into a multiplication (which most people find easier than division):

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85 × 3 = 255

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