if i pick 10 numbers from a possible 80.

what is the probablity for someone else picking the same 10 numbers as me? or just 4 numbers? or no numbers?

i think it's no matches: 10/80 one match: 10*9/80*79

so the formula would be (10!/matches!)/(80!/matches!)

is this right? i've only just started doing this at A-level and i need it for a game script i'm making.