Chapter 3 · Decimals and percents · page 13 of 68
Adding and subtracting decimals
levelPre-algebra
standard6.NS.B.3
practiceDecimals and percents
A decimal is a fraction with 10, 100 or 1000 underneath. Adding only works when the place values match, so the decimal points have to line up, not the last digits.
How to use it
- Write the numbers with the decimal points in a column.
- Fill empty places on the right with zeros so both have the same number of decimal places.
- Add or subtract as whole numbers, then bring the decimal point straight down.
Example
Where it goes wrong
- Lining up the last digits: 0.5 + 0.25 is not 0.30.
- Forgetting that a whole number has a decimal point after it: 3 is 3.0.