The method for subtracting fractions is very similar to the method for adding fractions. The key point is that you have to make the denominators (the bottom numbers) equal before you carry out the subtraction.
There are 5 simple steps to follow to subtract any fraction from another. It’s only as many as 5 because in some cases you have to deal with mixed numbers (a combination of a whole number and a fraction) and improper fractions (a fraction where the top number or numerator is greater than the denominator or bottom number).
Video Worked Example: How to Subtract Fractions in 5 Simple Steps
This video steps through the 5 steps. For best results, watch the video and then read through the text below:
Subtracting Fractions Worked Example
This worked example shows the five steps:
2¼ — 3/7
Step 1: If you have a mixed number convert it to an Improper Fraction
2¼ — 3/7 = 9/4 — 3/7
Step 2: Find a common denominator
9/4 — 3/7
Sometimes a common denominator will be obvious. However, we need a fool proof method. Simply multiply the denominators.
So, using our example, our denominators are 4 and 7 so we know that a common denominator will be: 4 x 7 = 28
Step 3: Convert the Numerators
For each fraction we need to multiply the numerator by the same amount as we multiplied the denominator. In this example we have
9/4 — we have to multiply the denominator by 7 to get to the common denominator of 28. Therefore we also have to multiply the numerator by 7 to give 9 x 7 = 63
3/7 – we have to multiply the denominator by 4 to get to the common denominator of 28. Therefore we also have to multiply the numerator by 4 to give 3 x 4 = 12.
So we have converted 9/4 — 3/7 to 63/28 — 12/28
Step 4: Subtract one Numerator from another
This is straightforward as you might imagine:
63/28 — 12/28 = 51/28