Definition
Decimal addition
Decimal addition finds a total by combining numbers written in decimal notation, matching each place value with the same place value.
What it means
Line up the decimal points so matching places stand in the same column. You may write a trailing zero to show a missing place. Then add as usual, regrouping ten of one place as one of the place to its left.
Remember it
Match the places, then add: the decimal points are landmarks that keep the columns true.
Example
3.48 + 0.70 = 4.18. The hundredths give 8. The tenths give 4 tenths + 7 tenths = 11 tenths, so regroup 10 tenths as 1 one. Then 3 ones + 1 regrouped one = 4 ones.
Watch for
Writing 0.7 as 0.70 does not change its value; the extra zero only makes the hundredths place visible.
Common mix-up
Do not line up the last digits. Line up the decimal points so each digit stays with its own place value.
Exact meaning
Decimal addition adds numbers written in decimal notation to find their sum. Each place value is combined with the same place value—ones with ones, tenths with tenths, hundredths with hundredths—and regrouping follows base-ten structure.