Adding and Subtracting Decimal Numbers
Grade 8 math lesson on adding and subtracting decimal numbers with and without regrouping. Students learn to align decimal points, add or subtract column by column, and handle carrying and borrowing across the decimal point.
Key Concepts
Performing arithmetic with decimal numbers is similar to whole numbers, but with one key rule. The most important step is to align the decimal points before you add or subtract. What’s next.
Let's put this rule into action. You'll soon tackle worked examples and word problems that sharpen your computational accuracy with decimals.
Common Questions
How do you add decimal numbers?
Line up the decimal points vertically so that digits in the same place value are aligned. Add each column from right to left, carrying when the sum exceeds 9. The decimal point in the answer goes in the same column as the others.
How do you subtract decimal numbers?
Line up the decimal points. Subtract each column from right to left, borrowing from the next column when needed. Place the decimal point in the answer directly below the decimal points in the problem.
What do you do if decimals have different numbers of places?
Add zeros to the end of the shorter decimal so both have the same number of decimal places. For example, to subtract 3.4 from 5.27, write 3.4 as 3.40 before subtracting.
Why is it important to align decimal points when adding or subtracting?
Aligning decimal points ensures you are adding or subtracting digits with the same place value. Adding tenths to hundredths without aligning would give a completely wrong answer.