Decimals are an essential part of world of math and subtracting them is one of the primary manipulations. Plus, decimals are money. Subtracting decimals requires practice before moving on to more complicated topics that may turn up on your exam.
You will need these to perform operations on the actual math GED® exam.
The Idea of Borrowing
The problematic concept for subtracting decimal numbers involves borrowing. During this process, you can take a group from the next column to the left of a number. This process drops the number you borrowed from drop by one (most people put a slash through it), and the original column that necessitated borrowing gain 10. Most people denote this with a small 1 above the number.
The borrowing process can be repeated as many times as necessary throughout a problem. It’s important to note that borrowing is only required if you cannot complete a column without going into negative numbers. Additionally, you cannot borrow from a 0, and must perform further steps.
Steps for Subtracting Decimals
The first step in subtraction is lining up the numbers. Unlike addition, the order of the problem does matter, and mixing them up will give you the wrong answer. As you’re reading from left to right, the value on the left goes on top of the problem. The value to the right goes underneath. You line them up by the decimal.
The subtraction process for decimals begins on the right side with the values. Your first step is asking if the number at the top of that column is bigger than the number below it. If it is, great, you don’t need to borrow. If it is not, you need to borrow from the next column to the left. Then you can subtract. Write the answer under that column. Then move to the next column to the left.
You can continue this process until you run out of columns to move to. At that point, you have your answer. If there is no value under a number, it is assumed to be a 0.
If you have three or more values in a decimal subtraction problem, it’s best to separate into separate operations. Begin with the two values in the problem furthest left. Once you solve those, subtract the third number from the answer. You can repeat this as needed.
Example Problems for Subtracting Decimals
Let’s start with a simple problem, 19.1-5. When we line up the problem, the 5 goes underneath the 9 and we’ll add a 0 under the .1. We first ask ourselves if 1 is bigger than 0, so we do the math and write the answer under the column. Then we can take 5 from 9, leaving us to write 4 under that column. Since there is nothing under the 1, we just drag it down. Therefore, the final answer is 14.1.
For our next example of subtracting decimals, let’s look at 2.9-1.3. When we’re lining up the numbers, the 3 goes under the 9 and the 1 goes under the 2. We start with the tenths column by asking ourselves if 9 is bigger than 3, which it is. We can subtract without borrowing, and we would write 6 under that column. Then we repeat the process with the ones column, writing 1 under there. The final answer is 1.6.
Now let’s talk about significant borrowing with 21-2.9. We’ll need to add a .0 to the 21 so everything lines up. We’ll start in the tenths place, which requires we borrow from the ones column. Then we’ll move to the ones column, which requires we borrow from the tens column. If you followed all that borrowing, the final answer is 18.1.