Decimal addition or subtraction sentences are math statements that show how decimal numbers are combined (added) or compared (subtracted) to find a result. Each sentence includes decimal numbers, an operation sign (+ or −), and an equal sign (=) to show the complete relationship.
4.25 + 3.5 = 7.75
8.6 − 2.15 = 6.45
We call them sentences because, like sentences in reading, they have a complete meaning: numbers, an operation, and an answer.
To add decimals, write the numbers so the decimal points are lined up. Then, add each column starting from the right, just like whole numbers. If the decimals have different numbers of digits, add zeros to make them the same length.
Double-check that all digits are in their correct place values. Adding zeros to the end of a decimal does not change its value.
To subtract decimals, line up the decimal points and subtract each column starting from the right. If necessary, add zeros so both numbers have the same number of decimal places.
Borrow from the next place value when a smaller number is on top. Remember that the decimal point in the answer should line up directly below the decimal points in the numbers above.
Sometimes, a decimal addition or subtraction sentence will have a missing part. You can find the missing number by using the inverse operation — addition and subtraction are opposites.
Check your answer by reversing the operation. If the new equation is true, your solution is correct.
After solving, always check your decimal addition or subtraction sentence by estimating. Round each number to the nearest whole number and make sure your answer is reasonable.
If your estimate and your exact answer are close, your decimal calculation is likely correct.