A card is drawn from a pack of 52 cards. The probability of getting a queen of club or a king of heart is:

x₁,x₂,x₃,…,x₅₀are are  fifty real numbers such that x_r < x_r+1 for r = 1, 2, 3... 49. Five numbers out of these are picked up at random. The probability that the five numbers have x₂₀ as the middle is:

A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement from the box, what is the probability that the sum of the three numbers on the balls selected from the box will be odd?