Question 1079212
So look at the number of possible codes.
Assume you can repeat letters and digits.
{{{N=26*26*10*10*10*10=6760000}}}
a) Only one of those outcomes is correct so 
{{{P=1/6760000}}}
b) Again only one is correct, all others incorrect,
{{{P=(6760000-1)/6760000=6759999/6760000}}}
c)So then the number of outcomes reduces to {{{N=10*10*10*5=5000}}} so the probability of guessing correctly is,
{{{N=1/5000}}}
d) Classical