Query about question "Given that $x$ and $y$ are prime numbers..." [130]

GRE GRE Quant Problem Solving
1

https://www.gregmat.com/problems/quant?problem=given-that-x-and-y-are-prime-numbers

Why do we assume that x and y are different from each other?

2

Those helped Greg choose correct answers. If you can arrive at answers assuming x=y, you can certainly use that.