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It's
not too hard to subtract small numbers from each other. |
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You
can count on your fingers. |
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You
can picture small objects in your mind. |
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Stuff
like that. |
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But
sooner or later, you will run into something a bit bigger: |
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(Hmmm,
didn't they say something like that about the Titanic?) |
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Example: |
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Nobody
from this planet has THAT many fingers. |
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We
need a new plan to deal with this puppy. |
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Here's
what we do: |
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Start with
the numbers on the right.
Subtract the three from the 8.
8 - 3 = 5
So write down the 5. |
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Now move
one column to the left.
Subtract the 2 from the 5.
5 - 2 = 3
Write down the 3. |
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Move left
again and subtract.
There is no lower number in this column.
That works like a zero.
3 - 0 = 3
Write down the 3. |
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That
worked great, |
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but
what if you have something like this: |
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Start like
before
with the numbers on the right side.
2 - 1 = 1
Write down the 1 |
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Now move
one column to the left
1 - 3 = UGH!
We have a problem!
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Yep,
we sure do. |
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We
need to have at least a three in the top number to do the
subtraction. |
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So
fine, are we stuck? |
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NEVER!
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We
can borrow 10! |
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Borrow
10? So where do we get it from? |
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From
the next column over to the left. |
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It
has at least a 1 in it, that 1 is worth 10 in the column we're
in. |
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Just
go borrow it! |
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Can
we do that? |
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Sure,
no problemo. Just watch: |
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Borrow the
1
that's in the next column to the left.
If we add it to the one we have, we get 11.
Remember, THAT 1 is worth 10 in this
column.
Now we can subtract.
11 - 3 = 8
Write down the 8. |
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Example: |
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OK,
Start with the numbers in the far right column.
7 - 3 = 4.
Write down the 4.
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Move one
column to the left.
0 - 6 = OOPS!
We need to borrow one
from the next column. |
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There is a
3 in the next column.
We don't need all 3.
We only need to borrow 1.
So take one and leave the other two.
Like this: |
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When we
bring the 1 into the middle column, it's worth 10.
Now we have 6 or more in this column so we can
subtract.
10 - 6 = 4
Write down the 4 and move on. |
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We now have
a 2 in this column.
Subtract the 1.
2 - 1 = 1
Write it down.
Since there's no more numbers,
we're done! |
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copyright 2005 Bruce Kirkpatrick |
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