A bag contains 5 white, 7 red 8 black balls. If four balls are drawn one by one with replacement, what is the probability that
(i) None is white
(ii) All are white
(iii) At least one is white
(i) Balls are drawn at random,
So, the probability that none is white is,
In a trial the probability of selecting a non-white ball is 
So, in 4 trials it will be,
⇒ (
)(
)(
)(
)= 
(ii) Balls are drawn at random,
So, the probability that all are white is,
In a trial the probability of selecting a white ball is 
So, in 4 trials it will be,
⇒ (
)(
)(
)(
)= 
(iii) Balls are drawn at random,
So, the probability that at least one is white is,
In a trial the probability of selecting a white ball is 
So, in 4 trials the probability that at least one is white is,
Selecting a white and then choosing from the rest,
⇒ 1-
that no ball is white
is 
.