Adding and subtracting with decimals
Adding and subtracting decimals happens a lot in real life. You may find that you need to add up the cost of your groceries to see if you have enough money to pay for them. Or perhaps you need to subtract the cost of a bill from your bank account.
When you're adding or subtracting decimal numbers, it's important to set up the expression correctly. The numbers need to be in a certain place, and so do the decimals.
Click through the slideshow below to learn how to set up these expressions.
First, let's set up an addition expression: 21.4 plus 6.82.
Just like with any addition example, we're going to stack one number on top of the other.
But instead of lining our numbers up on the right...
But instead of lining our numbers up on the right...we're going to line up the decimal points.
No matter how many numbers are on either side of the decimal point, we'll always line up the decimal points before adding.
Once we have the decimal points lined up, our decimals are ready to be added.
When we subtract decimals, we'll set up the decimals in the same way. Let's set up this example.
Instead of lining up our two numbers on the right, we'll line up the two decimal points.
And now our decimals are ready to be subtracted.
Now you try it. Write these situations as vertically stacked expressions. Don't solve them yet—just set them up.
You purchase two greeting cards. One costs $2.50, and the other costs $1.99.
Last week, you bought 3.75 gallons of gas for your car. This week, you bought 2.45 gallons.
You have $5.21 in your checking account. You pay $1.80 for your electric bill.
You have $9.99 in your pocket when you go to the mall. You decide to buy a shirt that costs $9.50.