Decimals

Adding decimal numbers

Now that we know how to set up problems with decimals, let's practice by solving a few. First, we'll work on adding. If you feel comfortable adding larger numbers, you're ready to add decimal numbers.

Click through the slideshow to learn how to add decimals.

• 

  Let's try solving this problem: 1.9 + 2.15.

• 

  First, we'll make sure the decimals are lined up.

• 

  We'll start by adding the digits farthest to the right. In this case, we have nothing on top and 5 on the bottom.

• 

  Nothing plus 5 equals 5. We'll write 5 beneath the line.

• 

  Now we'll add the next set of digits to the left: 9 and 1.

• 

  9 + 1 equals 10, but there's no room to write both digits in 10 underneath the 9 and 1. We'll have to carry.

• 

  We learned how to carry numbers in the lesson on Adding Two- and Three-Digit Numbers.

• 

  We'll write the right digit, 0, under the line...

• 

  We'll write the right digit, 0, under the line...then we'll carry the left digit, 1, up to the next set of digits in the problem.

• 

  Now we'll write the decimal point. We'll place it directly beneath the other two decimal points.

• 

  Next, we'll move left to add the next set of digits: 1 and 2. Since we carried the 1, we'll add it too.

• 

  1 + 1 + 2 equals 4. We'll write 4 below the line.

• 

  We're done. 1.9 + 2.15 = 4.05. We can read this answer as four and five-hundredths.

• 

  Let's try it with a money problem: $51.99 + $25.32.

• 

  We'll make sure our decimal points are lined up properly.

• 

  As always, we'll start by adding the digits on the right. Here, that's 9 and 2.

• 

  9 + 2 equals 11, so it looks like we'll have to carry.

• 

  The 1 on the right stays underneath the 9 and the 2.

• 

  We'll carry the 1 on the left and place it above the next set of digits to the left.

• 

  Now we'll move left to add the next set of digits. Since we carried the 1, we'll add it too.

• 

  1 + 9 + 3 = 13.

• 

  We'll put the 3 under the digits we added.

• 

  We'll carry the 1 and place it above the next column to the left.

• 

  Now it's time to write the decimal point. Remember to place it directly beneath the other two decimal points.

• 

  Next, we'll move left and add the next set of digits. We'll make sure to add the 1 we carried.

• 

  1 + 1 + 5 = 7. We'll write 7 beneath the line.

• 

  To finish, we'll add the next column to the left: 5 and 2.

• 

  5 + 2 equals 7. We'll write 7 underneath the 2.

• 

  We'll finish by writing the dollar sign ($).

• 

  We're done. $51.99 + $25.32 = $77.31. We can read this answer as seventy-seven dollars and thirty-one cents.

• 

Now you try it. Try solving these problems to practice adding decimal numbers.