How do you subtract fractions?

Question

My sister has the problem

8 - 2 1/3

& i dont know how to explain to her!

Answer 1

The other two answers are both valid ways of tackling such a problem.  If you opt for the improper fraction route, the trick I learned was to make a check over the mixed fraction (the 2 1/3) (one like this: http://upload.wikimedia.org/wikipedia/co... ).  Then follow it, the same way (most people) write it: multiply the 2 by the 3 (on your paper, those two will connect first with the check mark), and then add the 1 (the tail end of the check mark).  

But better than memorizing some ritualistic way of doing this, perhaps it would help to think of it conceptually.  I'm craving pizza, so we'll use pizzas.

If I had 8 pizzas, but then someone swiped 2 1/3 pizzas, how many would I have?  Hmmm...

Well, they swiped 2, so 8 - 2 = 6 ... but they swiped more than that, so I have less than 6 pizzas left.  How much less?  1/3 of a pizza less.  Can you see it in your head?  Having 6 pizzas and then having 1/3 of one of them gone?  And now can you count in your mind's eye (or on paper, if you drew it out) that there are 5 2/3 pizzas left?  Or have I just confused you more?  

Either way, good luck, and enjoy it!  

Answer 2

Mm... To subtract fractions, you need two fractions, and the numbers at the bottom of both fractions have to be the same.

In this case, 8 has no fractions right? So you have to make a fraction for it. How do you do that? Well, you should know that 8 = 7+1 right? And you should know that 1 = 3/3 (we use 3/3 in this case because the bottom number of the other fraction is 3. 1 is also equal to 1/1, 2/2/, 4/4/, etc.)

So it become 7 3/3 - 2 1/3

You minus the whole numbers and the fractions separately.

7 minus 2 is 5

3/3 - 1/3 is 2/3

So, the final answer is 5 2/3.

Note: when subtracting fractions, the bottom numbers have to be the same, and they don't change. The top number change.

Answer 3

First, convert to improper fractions to get:

8/1- 7/3

Then, make common denominators

8/1(*3)- 7/3 to get

24/3- 7/3.

Then subtract to get

17/3

Then make it mixed to get 5 2/3