Look at what's printed on the front or around the edge of the lens. According to
this page, it'll say "AUTO MACRO" if it's the 50/3.5 or 50/2 Macro. The
1:x means that the maximum aperture of the lens is f/
x.
It's most likely that one of the 50s is a 50mm f/1.8--that was the old kit lens that came with the camera back in the day.