Adding and Subtracting Decimals
Learning Outcomes
- Add decimals
- Subtract decimals that require borrowing
Adding Decimals
Let’s take one more look at the lunch order from the start of Decimals, this time noticing how the numbers were added together.
All three items (sandwich, water, tax) were priced in dollars and cents, so we lined up the dollars under the dollars and the cents under the cents, with the decimal points lined up between them. Then we just added each column, as if we were adding whole numbers. By lining up decimals this way, we can add or subtract the corresponding place values just as we did with whole numbers.
Add or subtract decimals
- Write the numbers vertically so the decimal points line up.
- Use zeros as place holders, as needed.
- Add or subtract the numbers as if they were whole numbers. Then place the decimal in the answer under the decimal points in the given numbers.
example
Add: . Solution| Write the numbers vertically so the decimal points line up. | \begin{array}{c}\hfill 3.7\\ \hfill \underset{\text{_____}}{+12.4}\end{array} |
| Place holders are not needed since both numbers have the same number of decimal places. | |
| Add the numbers as if they were whole numbers. Then place the decimal in the answer under the decimal points in the given numbers. | \begin{array}{c}\hfill \stackrel{1}{3}.7\\ \hfill \underset{\text{_____}}{+12.4}\\ \hfill 16.1\end{array} |
try it
[ohm_question]146586[/ohm_question] [ohm_question]146587[/ohm_question]example
Add: .Answer: Solution
| Write the numbers vertically so the decimal points line up. |  |
| Place as a place holder after the in , so that both numbers have two decimal places. |  |
| Add the numbers as if they were whole numbers. Then place the decimal in the answer under the decimal points in the given numbers. |  |
try it
[ohm_question]146588[/ohm_question]Subtracting decimals
example
How much change would you get if you handed the cashier a $20 bill for a $14.65 purchase? We will show the steps to calculate this in the next example. Subtract: .Answer: Solution
| Write the numbers vertically so the decimal points line up. Remember is a whole number, so place the decimal point after the . |  |
| Place two zeros after the decimal point in , as place holders so that both numbers have two decimal places. |  |
| Subtract the numbers as if they were whole numbers. Then place the decimal in the answer under the decimal points in the given numbers. |  |
try it
[ohm_question]146590[/ohm_question]example
Subtract: .Answer: Solution If we subtract from , the answer will be negative since . To subtract easily, we can subtract from . Then we will place the negative sign in the result.
| Write the numbers vertically so the decimal points line up. |  |
| Place zero after the in as a place holder, so that both numbers have two decimal places. |  |
| Subtract and place the decimal in the answer. |  |
| Remember that we are really subtracting so the answer is negative |
