Out of 50 consecutive natural numbers, two integers are chosen at random. What is the probability that their sum is odd?

Let X be a random variable following binomial distribution with parameters n = 5 and p = k Further, P(X = 1) = 0.4096 and P(X = 2) = 0.2048 . What is the value of k? 

If P(A) = 0.3 , P(B) = 0.4 and P( A |B)=0.5, then what is the value P( B |A) ?
 

If P(A) = 1/3 , P(B) = 1/2 and $ P(A\cap B)=1/4$ , then what is the value of $P(\overline{A}\cup B)$ ?