Let p, the probability of throwing doublet i.e., {(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)} with a pair of dice =

6

36

=

1

6

, then q=1−

1

6

=

5

6

X has a binomial distribution with n−4,p=

1

6

,q=

5

6

∴ Probability of getting 2 successes =P(X=2)=4C2q2p2 =6×(

5

6

)2×(

1

6

)2=

25

216