A discrete random variable X takes values 10, 20, 30 and 40. with probability 0.3, 0.3, 0.2 and 0.2 respectively. Then the expected value of X is

Let $$X$$ be a random variable which takes values $$1,2,3,4$$ such that $$P(X=r)=K r^3$$ where $$r=1,2,3,4$$ then

12 balls are distributed among 3 boxes, then the probability that the first box will contain 3 balls is

A random variable X has the probability distribution

For the events E = {X is a prime number} and F = {X < 4}, then P(E $$\cup$$ F) is