.
(0) The basic version
The number of all possible outcomes is 10*10*10*10 = .
It means that, in all, = 10000 tickets were issued.
So, the probability to win having one ticket is P = = = 0.0001.
version (i)
The number of all possible outcomes is 10*9*8*7 = 5040.
It means that, in all, 5040 tickets were issued.
So, the probability to win having one ticket is P = = .
version (ii)
The number of all possible outcomes is = = 6*10*9*8 = 4320.
It means that, in all, 4320 tickets were issued.
So, the probability to win having one ticket is P = .
Version (iii)
The number of all possible outcomes is = = 6*10*9 = 540.
It means that, in all, 540 tickets were issued.
Thus, the probability to win having one ticket is P = .
Solved.