Posted by Peter on 11th February 2009

Maths worksheet: Subtracting a decimal from a whole number

subtract-a-decimal-from-a-whole-number-1Subtracting a decimal number from a whole number can be done ‘in your head’ if it only involves tenths, usually by ‘counting on’ .

A good knowledge of pairs of numbers which make 10 really helps here.

Let’s look at:

1 – 0.3

Probably the easiest way to do this is by ‘counting on’.

Step 1:  Count on from 0.3, in tenths   up to one.

(eg 0.4, 0.5, 0.6 …etc

which comes to  0.7

1 – 0.3 = 0.7

Of course, if you know that 7 + 3 makes 10, then you can transfer this knowledge ie 0.3 + 0.7 = 1
In the same way:

4 – 3.3 = 0.7

Watch out for the answer 1.7 to the above question which is incorrect and shows a lack of understanding of numbers and ‘counting on’.

Subtract a decimal from a whole number (1)

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