When adding or subtracting decimals, make sure the decimal points are above each other when working in columns.
Not all numbers may have the same number of digits after the decimal point; add zeroes at the end of numbers to make them all the same length.
When the columns are lined up, the answer will have a decimal point in the correct place.
1. Add 23.2, 0.55 and 18.
Add a zero to the end of 23.2, and a decimal point and 2 zeroes to the end of 18 (this does not change their values) to make all the numbers the same length. Line up the decimal points, then add as usual. The decimal point in the answer will be in the same column as the other decimal points.
2. Subtract 8.322 from 11.5.
Add zeroes at the end of 11.5 to make the numbers the same length. Keep the decimal points in line; the decimal point will then be in the correct position for the answer.