Question

A box contain 4 red and 3 black ball. One ball is taken away from the box. After that two balls are drawn at random and both found red, what is the probability that the first ball taken always was also red?

(a) (2/5)

(b) (4/7)

(c) (24/105)  

(d) None

Answer 1

The correct option (a) (2/5)

Explanation:

Total 4 red and 3 black balls.

given: 2^nd & 3^rd balls are red. i.e. possibility of getting 1 red ball in 1^st 

chance is out of 2 remaining red balls. 

∵ These are two independent events, probability of getting 

1 red ball from 2 red + 3 black balls is [(²C₁)/(⁵C₁)] = (2/5).