9 Subtracting small numbers
If you want to subtract without using a calculator, you need to know off by heart what you get if you subtract any number up to 10 from any bigger number up to 20. All the possible combinations are shown in the table below.
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Say you want to subtract 6 from 13. You look up 13 in the top row, and –6 down the leftmost column. The answer is shown where the 13 column lines up with the –6 row, so in this case the answer is 7.
In other words, the top row shows the number you want to start with. The leftmost column shows the number you want to subtract from your starting number. The result of the subtraction is shown where the row and column cross.
If you want to, you can use this table to practise remembering all the possible combinations. There is an interactive version of the table on the Subtract page of the Numbers website, which you might find helpful.
To help you remember you can also do some practice calculations if you want. Go to the Practice sums page of the Numbers website and select Subtraction from the pull-down list next to Type of sum.Type of sum. Then follow the instructions on the page.
This web page can also give you practice in addition, multiplication or division if you want. Select the appropriate option from the Type of sum menu.