He just wanted to explain that it would be totaly useless to provide a hack with non working functions. So his calculation actually makes sense.
30 Functions -> with just 10 working = A 10 Function hack | 10 Functions -> A 10 Function hack. So it's just common sense to remove patched/disabled Functions
You did'nt get it either bra, he said 30 functioned hack with 10 non working . That makes the other 20 functional / working .