Adding Decimals

Adding decimals is a fundamental skill for you on your exam. It also applies in real life, since all money is in decimals. Adding decimals is similar to adding whole numbers, except it’s lined up slightly differently.

Necessary Skills

Depending on the problem, the below skills may be necessary. You will need them on an actual math GED® exam.

The Idea of Collecting

The difficult central concept for adding decimals involves collecting. Collecting the mathematical term for what you may have learned as carrying in school. During this process, if a column adds up to more than ten, then you write the ones place down and bring the tens place to the next column to the left. Do not carry more than one column.

This process repeats as often as necessary since each column is its own step in an addition problem. It’s vital that you do not confuse the places, since writing the tens spot and carrying the ones spot will lead to a wrong answer.

Decimal Place Values

The Steps for Adding Decimals

The first step with any addition problem is setting up the places into columns. You will need to line numbers up based on the decimal, which is to the right of the ones place. Any space that does not have a number in it is assumed to be a zero.

Once all the columns line up neatly, it’s time to perform the actual math. You will start with the rightmost column and ignore the other columns until you’re done with that one. Add the two numbers together. If the number is less than 10, simply write it below the column. If the number is 10 or higher, you will need to carry. Then you move into the next rightmost column and repeat.

If you want to add more than two numbers at a time (ex. 2.3+4.5+2.1), you have two options. You can add the first two numbers, get that answer, and then add the original third. Your second option is to combine all three at the same time, which works if you make sure you’ve lined all the numbers based on the ones spot.

Example Problems for Adding Decimals

Let’s start with a simple problem, 2.5+3. When we line this up, the 3 will go under the 2 and a 0 would be written under the 5. To begin, we would add the 5 and the 0, for a total of 5. Since that’s less than 10, we can simply write it down. Then we add the 2 and the 3 for a total of 5, which we write under that ones column. That makes the answer 5.5.

Adding Decimals Example 1

Another example of adding whole numbers is 2.3+4.5. We would line this up so that the 5 is under the 3 and the 4 is under the 2. Since we start from the tenths column, that’s 8. That’s less than 10, so there’s no carrying. Then we add the 2 and the 4 in the ones column, which comes to 6. That makes our final answer 6.8.

Adding Decimals Example 2

Now let’s do a little collecting with 123+19.1. We’ll add a .0 to the 123 so everything lines up. We’ll start from the tenths spot with 0 plus 1. Then it’s 3 plus 9, which is 12. We’ll carry the 1 and write the three under the ones column. Then it’s on to the 2 and the 1, plus the carried 1. That’s 4, so no carrying. We’ll bring the leftmost 1 straight down. That makes our final answer 142.1.

Adding Decimals Example 3