Teresa gave away 8 baseball cards and has 4 left. 8 plus 4 means she originally had 12. Right now she has 4 out of her original 12 cards remaining. This gives us 4/12. We can simplify this by dividing our greatest common factors. 4 goes into both parts of our fraction, when we divide each part by 4 we end up with 1/3. Since we are unable to simplify this problem any further, this means our solution and fraction is 4/12 aka 1/3.
