Question

A bag contain $15$ balls out of which ${}^{\prime }{y}^{\prime }$ are red
(i) if one ball is drawn at random,what is the probability that it is a red ball
(ii) if $5$ more red balls are put in the bag,the probability of drawing red ball will be double than that in (a) find number of red balls now in the bag.

Answer 1

Total number of balls in a bag $=15$

number of red balls $=y$

(i) p(red ball is drawn at random)$=\frac{y}{15}$

(ii) number of red ball added into the bag $=5$

total no of ball in bag $=20$

and no of red ball $=y+5$

now, p(drawing red ball randomly $=\frac{y+5}{20}$

A/Q; $\frac{y+5}{20}=2\left(\frac{y}{15}\right)\Rightarrow y=3$

therefore no of red ball $=3$