Question

A bag contains 2 red, 3 green and 2 blue balls. Two balls are drawn at random. What is the probability that none of the balls drawn is blue? 

Answer 1

The total number of balls is

$$2+3+2=7$$

The number of balls which are not blue is $2+3=5.$

The probability that the first ball is not blue and the second ball is bot blue is

$$P(B'B')=\dfrac{5}{7}(\dfrac{5-1}{7-1})=\dfrac{10}{21}$$

The probability that none of the balls drawn is blue is $\dfrac{10}{21}$ .