When we subtract a positive number from another positive number, we move towards the left on the number line.
For example, let's consider the following subtraction problem:
To subtract from we start at on the number line and move places to the left.
When we do this, we land at Therefore,
What is the value of
To subtract from we start at on the number line and move places to the left.
When we do this, we land at Therefore,
$0 - 8=$
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a
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$-8$ |
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b
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$8$ |
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c
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$0$ |
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d
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$\dfrac{1}{8}$ |
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e
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$-\dfrac{1}{8}$ |
It is impractical to use number lines to subtract large numbers.
However, a neat trick makes subtracting a positive number from a smaller positive number very easy!
As an example, let's consider the following subtraction problem:
Since is larger than the answer must be negative.
We start by solving an easier problem: subtracting the numbers in the reverse order. In our case, the reverse problem is
Next, we carry out the subtraction:
So, we have
However, since our answer must be negative, we need to change the sign of the answer above.
Therefore, we conclude that
And that's it!
Let's use the same idea to subtract two three-digit numbers.
Find the value of
Since is larger than the answer will be negative.
We start by solving an easier problem:
Next, we carry out the subtraction:
So, we have
However, since our answer must be negative, we need to change the sign of the answer above.
Therefore, we conclude that
$12 - 36=$
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b
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c
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d
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e
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$69 - 103=$
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a
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$-44$ |
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b
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$36$ |
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c
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$34$ |
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d
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$-36$ |
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e
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$-34$ |
$206 - 364 = $
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a
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b
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c
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d
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e
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