Subtraction – formal and informal methods

There are both informal and formal methods of subtraction.  Those shown here are similar in layout to those used for carrying out addition.

An informal method of subtraction

This informal method of subtraction is base on using a number-line and counting on to find out the difference between two numbers.  It is very similar to the informal method used for carrying out addition.

A formal method of subtraction

This formal method of subtraction uses columns.  (see formal method of addition)  However, when subtracting,  number order is important and will make a difference to the result.


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