How to Borrow Fractions

If you know how to subtract whole numbers using borrowing you can also subtract fractions with borrowing. The key is to take it one step at a time. Here are instructions for borrowing fractions.

Instructions

1. 

   Decide if you need to borrow. First make sure the denominators are the same. Let's use the sample problem 6-1/2 - 3-5/8. In this case the denominators are not the same, so you have to convert the fractions to make the denominators match. First you need to find the Lowest Common Denominator (LCD), which is 8. The second fraction already has a denominator of 8, so you will need to change the denominator in the first fraction.

2. 

   Make your denominators the same by multiplying the top and bottom of the first by the same number. You would change the fraction 1/2 to 4/8 by multiplying the numerator and the denominator by 4. This changes your problem to 6-4/8 - 3-5/8.

3. 

   Compare your fractions. You will see that in this problem you are trying to subtract 5/8 from 4/8. This cannot be done. You will have to borrow.

4. 

   You are borrowing from the whole number next to the first fraction to make the fraction bigger. Just as you would do in a simple subtraction problem, you will have to borrow a 1 from the number in front of it. So your 6 becomes a 5, and you have to turn the 1 into a fraction. To equal 1 and to match your existing fraction, your numerator and denominator both have to be 8. It will look like this:6-4/8 - 3-5/8(5 + 1 + 4/8) - 3 -5/8(5 + 8/8 + 4/8) - 3-5/85-12/8 - 3-5/8

5. 

   Add your new fraction and your existing fraction. Now you are ready to subtract your fractions. 5-12/8 - 3-5/8= 2-7/8

Tips & Warnings

• Do not skip any steps, or you may make an error.