Fraction Project

Adding and Subtracting Fractions

First, I'm going to teach you how to get the sum of fractions with like denominators, then with unlike denominators, and then with mixed numbers:

LIKE Denominators:

Lets say the question is 1/5 + 2/5. All you have to do is add the numerator and the other numerator.

So, 1/5 + 2/5 = 3/5.

NOT: 1/5 + 2/5 = 3/10.

In adding with LIKE denominators you never add the denominators. Only the numerators it would make a BIG difference in your answer.

If your sum comes out to be an improper fraction, we have to change it into a mixed number which is putting it in lowest terms.

Lets say this was your answer: 8/5. Since the numerator is larger then the denominator it is called an improper fraction. To convert it back into a proper fraction. This is what you have to do:

Ask yourself "How many times does 5 go into 8?"


5 goes into 9 one time. Then you take the 3 and put it over the 5. So your final answer should come out to be 1 3/5.

The same exact thing is with subtracting.

Lets say the question is 4/5 - 3/5.

All you have to do is - 4 from 3. So that makes the answer 1/5!


UNLIKE Denominators:

When adding with Unlike Denominators, you first have to find something called the LCD (least common denominator).

So lets say the question is 3/5 + 2/4.

This is when we find the LCD.

5, 10, 15, (20),

4, 8, 12, 16, (20),

 3/5 = /20


 2/4 = /20

So now we have two denominators with no numerators. What we do to the bottom we have to do to the top so our problem now is 12/20 + 10/20. all you do is add across with the numerators and we now have 22/20.

22/20 is converted to 1 1/10.

Lets say there is a whole number - a fraction. This is what you have to do:





Alright, first we have to make 20 into a fraction, so to do that, we cross it out, and put a 19 above it. Because we are borrowing from it. Then we put 20/20 next to the 20. Now we subtract.






Converted to 1 1/4.



Mixed Numbers:

Lets say the question is 5 1/3 + 3 1/4.

We have to find a LCM for 4 and 3 so that would be 12 so now its and whatever you do to the bottom you have to do to the top so its now




That would = 7/12.

Now, we go back and add 5 and 3 and that is 8 so now the answer is 8 7/12.