Arithmetic Grade Four
Lesson Thirty-two: Subtraction
Look at this subtraction problem:
The problem with this kind of subtraction problem is that you cannot just
subtract the one's column since 2 - 8 will give us a negative number. Since
the tens column has a digit in it we can borrow ten from it. When we borrow
ten from the tens column we wind up with an altered problem that looks sort
of like this:
tens | ones
--------|---------
2 | 12
- | 8
-----------------
2 | 4
So, 32 - 8 = 24.
Obviously, you could have solved the problem 32-8 by counting backwards 8,
but with really big problems like:
counting backwards isn't a very good way of solving the problem. In a couple
lessons we will deal with problems like these, but for now we will stick to
simpler problems.
Here's another easy example:
In the ones column 4 - 7 isn't going to work for us and so we will borrow
one from the tens column (which will leave a 3 in the tens column and make
14 in the ones column).
3 | 14
- | 7
------------
3 | 7
Now you will try a few of these yourself.
Click here to go to next page