An urn contains 10 black and 5 white balls. Two balls are drawn from the urn one after another without replacement. What is the probability that both balls drawn are black ?

A bag contains $5$ red, $6$ white and $7$ black balls. Two balls are drawn at random. What is the probability that both balls are red or both are black?

There are $2$ red and $3$ black balls in a bag. Three balls are taken out at random from the bag. Find the probability of getting $2$ red and $1$ black ball or $1$ red and $2$ black balls.

From a bag containing $20$ tickets, numbered from $1$ to $20$, two tickets are drawn at random. Find the probability that

both the tickets have prime numbers on them

From a bag containing $20$ tickets, numbered from $1$ to $20$, two tickets are drawn at random. Find the probability that

on one there is a prime number and on the other there is a multiple of $4$.

An urn contains $4$ red and $7$ blue balls. Two balls are drawn at random with replacement. Find the probability of getting $2$ red balls.

An urn contains $4$ red and $7$ blue balls. Two balls are drawn at random with replacement. Find the probability of getting $2$ blue balls.