Total number of disc in a box , n(s) = 90
(i) Let E1= Evernt of selecting a two-digits number = {10,11,......90}
n(E1)=81
Probability of geting a two-digit number =
n(E1)
n(E2)
=
81
90
=
9
10
(ii) Let E2 = Event of selecting a number divisibel by 5
={5,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80,85,90}
∴ n(E3)=18
∴ Required probability =
n(E3)
n(S)
=
2
6
=
1
3
