This web page describes how to use the graph paper function to perform long subtraction. Long subtraction involves using the Borrow button to borrow numbers from the next number. Please review the article on long addition, as some general information is provided there.

Long Subtraction

The problem we are going to solve is shown below

Enter the problem in an identical way to long addition, except you should put a minus sign instead of an addition sign.

Now you want to subtract 3 from 4, but 3 is too small so what do you do? You borrow from the next number along. In this case you borrow from the 2. Press the Borrow button.

You will see the screen automatically updates in a similar way as if you are doing this by hand. The 3 becomes 13 and the 2 becomes 1.

Now work out the subtraction and press the 9 buttons which is the result

Now you see that 4 is too big to subtract from 1, so press the borrow button again. The 1 becomes 11 and the 4 becomes 3.

Work out the difference of 11 minus 4 and carry on for the next digit. As the final digit will be 5 – 5 which is zero, the process is finished.

Press the Copy button to move the result to the answer.

Special Cases of Subtraction

Borrowing from zero

If you find you need to borrow from zero you will not be allowed to do it. A message box will appear. For example

When you attempt to borrow from zero you will get this error message

The solution is to use a two step borrow. Firstly click on the next cell (below the digit 8) and press borrow to borrow from the 3.

Now click on the previous cell and borrow from the 10.

You can now proceed as before with the subtraction

Subtracting negative numbers

It is possible to configure the question generator program to generate subtractions with a negative result. If you find that you are subtracting a bigger number from a smaller number, for example

You should switch the values around when laying out the problem, as below

Solve the subtraction as normal

However before copying the result, you must remember to negate the result. Press the minus button.

To give

You can now finally Copy the result.