$A$ bag contains $5$ white and $3$ black balls. If two balls are drawn at random,what is the probability that one ball is white and the other is black?

There are four machines and it is known that exactly two of them are faulty. They are tested,one by one,in a random order until both the faulty machines are identified. Then the probability that only two tests are needed is

From out of $100$ enrolled students,two sections of strength $40$ and $60$ are formed. If you and your friend are among those $100$ students,then the probability that both of you are placed in the same section is

In a certain lottery,$10,000$ tickets are sold and $10$ equal prizes are awarded. What is the probability of not getting a prize if you buy $10$ tickets?

$A$ box contains $8$ red, $3$ white and $9$ blue balls. If $3$ balls are drawn from the box at random one after the other without replacement, then the probability that they are $2$ red balls and $1$ white ball is

Two tickets are drawn at random from tickets numbered $1$ to $20$. The probability that the numbers on both tickets are prime numbers is ..........