Decoding timetable group structures mmu

So I'm a first year electrical engineering student at mmu and made a few friends. None of us can figure out which classes we share together and we seem to be split in a random way. Like I'm in Group 05, and people in the same group as me sometimes share my math lessons and sometimes workshops and sometimes neither.
It's kinda annoying and i want to understand if theres a way to predict it?