$A$ box contains $3$ blue,$2$ white,and $4$ red marbles. If a marble is drawn at random from the box,what is the probability that it will be
$(i)$ white?
$(ii)$ blue?
$(iii)$ red?

(A) The statement that a marble is drawn at random implies that all marbles are equally likely to be drawn.
Total number of possible outcomes $= 3 + 2 + 4 = 9$.
Let $W$ denote the event 'the marble is white',$B$ denote the event 'the marble is blue',and $R$ denote the event 'the marble is red'.
$(i)$ The number of outcomes favourable to the event $W$ is $2$.
So,$P(W) = \frac{2}{9}$.
$(ii)$ The number of outcomes favourable to the event $B$ is $3$.
So,$P(B) = \frac{3}{9} = \frac{1}{3}$.
$(iii)$ The number of outcomes favourable to the event $R$ is $4$.
So,$P(R) = \frac{4}{9}$.
Note that $P(W) + P(B) + P(R) = \frac{2}{9} + \frac{3}{9} + \frac{4}{9} = \frac{9}{9} = 1$.