Adding and Subtracting Decimals

Adding and subtracting involving decimals is certainly best tackled after your child has grasped the concept of tenths and hundredths. You will find more on place value with tenths and hundredths here.

Assuming this concept is understood, then the essential step of lining up the decimal points when adding or subtracting should be more easily followed.

Illustration showing how the decimal points must be lined up when adding or subtracting numbers.

Be sure the decimal point is included in the answer

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When zero does not mean anything

You can review with your child how, when adding or subtracting whole numbers, zeros can be added to the left of a number without affecting its value.

Illustration of how adding zeros to the left of a number does not change its value.

The same logic can be applied to the tenths, hundredths, and thousandths using the base 10 blocks as a visual reference.

Illustration of why adding zeros to the right of digits that showing tenths, hundredths, thousandths, etc. does alter the value of the number.

This will help when adding and subtracting numbers with different numbers of digits.

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Common Errors When Adding & Subtracting Decimals

The example below shows a common mistake that is made when adding and subtracting with decimals.

example of common error when adding and subtracting with decimals

Lining up the decimal point when doing vertical addition or subtraction makes the calculation much easier. Adding zeros to the right of the decimal numbers may also be needed. When adding with decimals and whole numbers students may also have to add a decimal point on the right of the whole number. Finally, estimating the answer and comparing it with the calculated answer will help avoid errors that do not make sense.


happy face iconTry the decimals worksheet generator. It provides limitless adding decimals questions. It also provides questions on subtraction and multiplication too.

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