Here's one that's not too tricky to figure out where the problem is. 
Let
 x=y. 
Then 
x - y + y = y
x - y + y y
--------- = ---
x-y x-y
y y
1 + --- = ---
x-y x-y
1 = 0
Now we know that 1 = 1, so add the following three equations together:
1 = 0
1 = 1
1 = 1
On the right is 1+1, and on the left is 3 ones, and 3 ones make 3.