Take an example problem: 4.63 + 5.24.
Arrange the numbers vertically, making sure the decimal points are lined up:4.635.24 +--------
Add normally, making sure the decimal point lines up in the result:4.635.24 +-------9.87
If the addends have different numbers of decimal places, add zeros to the right to make them line up. Take an example problem: 4.63 + 2.1 + 3.
Arrange the numbers vertically with the decimal places lining up.4.632.1 +3 +-------
Add zeros to the right so that they'll have the same number of digits:4.632.10 +3.00 +--------
Add normally, making sure the decimal points line up:4.632.10 +3.00 +--------9.73
The same procedures apply to subtracting decimals. Take an example problem: 15 - .27.
Arrange the numbers vertically, lining up the decimal points. There is a decimal point after 15.15.00.27 ---------
Fill in with zeros. For whole numbers (15), adding zeros to the right of the decimal point does not change the value. For decimals less than 1 and greater than -1 (.27), adding zeros to the left of the decimal point does not change the value:15.0000.27 ---------
Subtract normally:15.0000.27 ----------14.73
So 15 - .27 = 14.73.