JEE Main Math Class 12 Probability Part 1 Questions

Let X be the random variable which denotes the Rs gained by the person.
Total cases =6×6=36
Favorable cases for the person on winning Rs.15 are (1,1),(2,2),(3,3),(4,4), (5,5),(6,6) i.e., 6 cases.
∴P(X=15)=

6

36

=

1

6

Favorable cases for the person on winning Rs.12 are (6,3) , (5,4),(4,5), (3,6) i.e., 4
∴P(X=12)=

4

36

=

1

9

Remaining cases =36−6−4=26
∴P(X=−6)=

26

36

=

13

18

Hence, E(X)=∑X.P(X)=

5

2

+

4

3

−

13

3

=−

1

2