Question

A bag contains 'a' white and 'b' black balls. Balls are drawn one by one until balls of one colour are completely drawn out. Then the probability that the experimental ends with black balls left in the bag is

• A. b/a+b
• B. a/a+b
• C. a-b/a+b
• D. 2a/a+b

Answer 1

Answer: (A)

b/a+b

Answer 2

N(s) = $\frac { \angle \mathrm { a } + \mathrm { b } } { \angle \mathrm { a } \angle \mathrm { b } }$ n(5) = $\frac { \angle \mathrm { a } + \mathrm { b } - 1 } { \angle \mathrm { a } \angle \mathrm { b } - 1 }$

P(5) = $\frac { \angle \mathrm { a } + \mathrm { b } - 1 \angle \mathrm { a } \angle \mathrm { b } } { \angle \mathrm { a } \angle \mathrm { b } - 1 \angle \mathrm { a } + \mathrm { b } } = \frac { \mathrm { b } } { \mathrm { a } + \mathrm { b } }$.