Lesson Plan - Get It!
Why does it matter if the denominator is different or the same when adding fractions? How do these crazy things work?
When we first start doing math, one of the beginning concepts is addition; for example, 2 + 2 = 4.
We simply put all of the values together to achieve our answer. When we advance through math and get to fractions, addition takes on a few more steps or rules.
- Why can't we just add all the values and go from there?
- Why does there have to be a common denominator?
First, let's remember that fractions are showing part of a whole, and that the two parts of a fraction are the denominator (how many pieces the whole is divided up into), and the numerator (the number of pieces we are working with).
That denominator is super-important! It must be the same for everything we are trying to add. If it isn't the same, it's as if we are looking at two different things, like apples and oranges. In order to add the fractions, the denominators must be the same. This video will help you see why common denominators are necessary. Watch WHY You Need Common Denominators by Mathbox7:
Explain to your teacher or parent why the denominators are important, how you go about getting the same denominators, and how that affects the numerators.
Now that we know why we need common denominators, let's figure out how to add fractions with like and unlike denominators!
This first video, Learn Fractions – Addition of Fractions by Appu Series, does a great job of showing you adding with both like and unlike denominators. It will start with a couple of examples of adding with like denominators. When you see the problem 2⁄9 + 3⁄9, pause the video and solve it on your own. When you have finished, resume and see if you're right!
Next up will be different denominators, again with a couple of examples. Don't be afraid to write them down as you're following along. When you get to the practice problem 2⁄3 + 2⁄7, pause it again and solve; then, resume. This next one is a little more fun!
Watch Mr. Austin and his class solve fraction addition problems in Denominators! (A song about how to add and subtract fractions), by Andrew Austin:
- Did you like how Mr. Austin used his rap to explain adding fractions with different denominators?
- What does LCM stand for?
- What was the LCM for the problem they were working on: 3⁄4 + 1⁄8?
- Once they found the LCM, what was the next step?
- Now, what did the fraction problem look like?
- What was their final answer?
- If you were to explain adding fractions, what steps would you break it up into?
Continue on to the Got It? section for some practice!