a single die is rolled 6 times. "Success" is getting a 3 or a 5. "Failure" is getting anything else. What is the probability of achieving exactly 2 successes in the 6 rolls?
P(success)=2/6 = 1/3
P(failure) = 4/6 = 2/3
number of ways you can get 2 successes and 4 failures in 6 rolls is 6C 2 ( 6C 4 gives exactly the same answer)
P(2 successes) = 6C2 * (1/3) 2 * (2/3) 4
= 15 * 1/9 * 16/81
= 80/243
+118628 
