When you ADD, things get bigger, longer or more.
Example
Jane has 12 pencils and Bill has 15 pencils.
How many do they have in total?
Answer
Add together 12 + 15.
Start at 12 and then add 10 and 5.
12 + 10 = 22
22 + 5 = 27
They have 27 pencils in total.
When you SUBTRACT, things get smaller, shorter, fewer or less.
Example
Jane has 27 marbles and gives 15 to her brother Bill.
How many does she have left?
Answer
Subtract 27 - 15.
Start at 27 and take away 10 then take away 5.
27 - 10 = 17
17 - 5 = 12
Jane has 12 left.