Answer: 2/3
Step-by-step explanation:
The mixed number 1 1/3 means that we have that first "1" as the whole part and the 1/3 as the fractional part.
We can think of it like having one full cake, plus a third of another cake. In other words: one full cake plus a small slice of another one.
The goal is to end up with two full cakes. To do this, we need to add on 2/3 because 1/3 + 2/3 = 3/3 = 1
That second cake is missing 2 slices needed to make it whole, so that's another way to see why the answer is 2/3.