I need some help with math.
there are 28 students in a class. there can be a 4 person group in the chorus. if chosen hoe many different combinations are possible? I don't know if to do 28(27)(26)(25) or 28+27+26+25 And 1 more question. teachers have a specific rule for a password. there are 2 letter an 4 numbers (0-9) how many different combinations are possible. thank you for the help