1/4 + 2/3 = 11/12 because you need to find the common denominator which is 12. You have to multiply 1/4 by 3 to get the denominator of 12, so it becomes 3/12. Then, you have to multiply 2/3 by 4 to get the denominator of 12 which gives you 8/12 so you add 3/12 + 8/12 and you get 11/12.
