Out of the first 20 positive integers, two are chosen at random. The probability that their sum is odd is:

A box contains 'x + 4' red, 'x – 1' green and 'x – 5' blue balls. If two balls are drawn from the bag one after another without replacement, then the probability of getting one red and one green ball is equal to the probability of getting a sum equal to or more than 8 when two fair dice are rolled. Find the probability of drawing a red ball when one ball is drawn at random from the bag.

Four persons are chosen at random from a group containing 3 men, 2 women, and 4 children. The probability that exactly two of them are children is:

A and B are two independent events such that P(A ∩ B) = 325 and P(A' ∩ B) = 825, then P(A) is:

A problem in statistics is given to three students whose chances of solving it are 12, 13 and 14 respectively. What is the probability that the problem will be solved?

n (≥ 3) persons are sitting in a row. Two of them are selected at random. The probability that they are not sitting together is:

If four whole numbers are chosen at random and multiplied together, what is the probability that the last digit in the product is 1, 3, 7, or 9?

If four whole numbers are chosen at random and multiplied together, what is the probability that the last digit in the product is 1, 3, 7, or 9?

Event A is called the complementary event of event B if A and B are ______.