Answer:
5/12
Explanation:
You would have to make the fractions equivalent.
Multiply both the numerator 1 and the denominator 4 by 3. You should end up with 3/12. For 1/3 you need to multiply the numerator 1 by 4 and the denominator 3 by 4. You should end up with 4/12. Add 3/12 and 4/12 and you should get 7/12. 7/12 is the amount they ate so you do 12 -7/12 which should get you 5/12.