Adding and Subtracting Decimals

Scroll down for further teaching material and practice exercises.

Video

When you are either adding or subtracting decimals, it is important to make sure that they are properly aligned. All of the thousands, hundreds, tens, ones, tenths hundredths, etc have to be placed one on top of each other in the proper order. For example if you were adding 256 to 1000.067 or subtracting 104.62 from 3020.001, the equation would have to be aligned as follows:

The easiest method of ensuring that the numbers properly align is to create decimal places so that all numbers share the exact same number of decimal places. Simply add zeros to each place value that does not have one until there are decimals places equal to all numbers in the equation. Then make sure the decimal point is directly above and below the decimal point for the other numbers.

Examples:

1) 103.991 + 35 =

The number 35 requires three decimal places (tenths, hundredths, and thousandths)

2) 78 – 5.21 =

The number 78 requires two decimal places (tenths and hundredths)

You’ll note in all of the equations the place values all line up with each other and all of the decimal points are in line as well.

Practice Exercises:

Solve the following equations (answers below).

1) 68.32 + 75.001 =

2) 105.72 – 104.73 =

3) 214 + 0.54 + 361.001 + 10 =

4) 105.88 – 48.32 =

5) 6198 + 81.78 + 0.215 + 200.04 =

6) 2415.21 – 101.1 =

7) 3 thenths + 2 hundredths + 65 =

8) 100.99 –1 =

9) 999.999 – 101.1081 =

10) 821.21 + 1000.001 + 100.01 + 10.1 + 1 =

Answers:

1) 68.32 + 75.001 = 143.321

2) 105.72 – 104.73 = 0.99

3) 214 + 0.54 + 361.001 + 10 = 585.541

4) 105.88 – 48.32 = 57.56

5) 6198 + 81.78 + 0.215 + 200.04 = 6480.035

6) 2415.21 – 101.1 = 2314.11

7) 3 thenths + 2 hundredths + 65 = 65.32

8) 100.99 –1 = 99.99

9) 999.999 – 101.1081 = 898.8909

10) 821.21 + 1000.001 + 100.01 + 10.1 + 1 = 1932.321