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Numbers, units and arithmetic
Numbers, units and arithmetic

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Addition and subtraction with decimals

Addition and subtraction can be carried out with decimals just as for whole numbers. Take care to write the numbers in their correct columns and keep the decimal points in line under each other.

Example 17

  • (a) Add 303.035 kg and 7.77 kg.

  • (b) Subtract 7.77 kg from 303.035 kg.


Remember to supply a ‘0’ at the end of 7.77 to keep the number of decimal places the same.

  • (a) The answer is 310.805 kg.

    multiline equation line 1 303.035 line 2 plus 7.770 line 3 310.805
  • (b) The answer is 295.265 kg.

    multiline equation line 1 303.035 line 2 minus 7.770 line 3 295.265

(With an awkward subtraction like this, a useful check is to add 7.77 to 295.265 to make sure that you get back to 303.035.)