Question

A bag contains a white and b black balls. A ball is drawn and the colour is noted, then it is replaced in the bag along with 'k' additional balls of the same colour. Then another ball is drawn is drawn. Then the probability that it is white is

• A. b/a+b
• B. a-b/a+b
• C. 1/a+b
• D. a/a+b

Answer 1

Answer: (D)

a/a+b

Answer 2

A be event of drawing white ball

B be of drawing black ball

Let E be event of drawing white after replacement.

P(1) = P(2)=

P(E/A) = $\frac { a + k } { a + b + k }$ P(E/B) = $\frac { a } { a + b + k }$

P(5)= $\frac { a ( a + k ) } { ( a + b ) ( a + b + k ) } + \frac { a b } { ( a + b ) ( a + b + k ) } = \frac { a ( a + b + k ) } { ( a + b ) ( a + b + k ) }$

P(5) = .