In our class in Mathematics lessons we continue to look at fractions. We are currently looking at subtracting fractions with different denominators.

So, here are the steps.

  1. Build each fraction so that both denominators are equal. Remember, when subtracting fractions, the denominators must be equal. So we must complete this step first. What this really means is that you must find what is called a Common Denominator. Most of the time you will be required to work the problem using what’s called the Lowest Common Denominator (LCD). In either case you will build each fraction into an equivalent fraction.
  2. Re-write each equivalent fraction using this new denominator
  3. Now you can subtract the numerators, and keep the denominator of the equivalent fractions.
  4. Re-write your answer as a simplified or reduced fraction, if needed.

Here’s a short video to show you how:

Can you answer the question below?

The Basics for Subtracting Fractions with Different Denominators

Subtract: 1/2 – 1/3

Notice that the overall size of our point of reference
(The Whole) is EXACTLY the same.

Step #1 in our rule tells us that the denominators must be equal. And the easiest way to find a common denominator is to just multiply the denominators.

So let’s do that now…

2 x 3 = 6

The Common Denominator for 1/2 and 1/3 is 6

Step #2 – Re-write each equivalent fraction using this new denominator.

Since…

1/2 is equivalent to 3/6

And…

1/3 is equivalent to 2/6

 

We re-write our equation to read…

Subtract: 3/6 – 2/6

Now we are ready to do Step #3 – Subtract the numerators, and keep the denominator of the equivalent fractions (which is 6).

So, we end up with…

3/6 – 2/6 = (3 – 2 )/6 = 1/6

=

Finally, Step #4 – Re-write your answer as a simplified or reduced fraction, if needed.

In our example, the answer (1/6) is already in its simplest form. So, no further action is required!

That’s It!

A quick and easy way to subtract fractions with different denominators.

Remember, always show your answer in the form asked for in your instructions.

Source: help with fractions

 

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