Question

There are $2$ white and $4$ black balls in an urn A and $4$ white and $7$ black balls in another urn B.One ball is transferred from urn A to B. Now one ball is drawn at random from B. The probability that it is white is

• A. $\frac{25}{39}$
• B. $\frac{15}{39}$
• C. $\frac{13}{36}$
• D. $\frac{14}{39}$

Answer 1

Answer: (C)

$\frac{13}{36}$

Probability of transferring white ball in $B=2/6=1/3$
In that case probability of drawing white ball $=5/12$
Probability of transferring black ball in $B=4/6=2/3$
In that case probability of drawing white ball $=4/12$
Required $P=1/3\ast 5/12+2/3\ast 4/12=13/36$