An urn contains 5 red and 5 black balls. A ball is drawn at random, its colour is noted and is returned to the urn. Moreover, 2 additional balls of the colour drawn are put in the um and then a ball is drawn at random. What is the probability that the second ball is red?

Explanation

let event of drawing red ball is R

let event of drawing black ball is B

probability = (R,R) + (B,R)

probability = `5/10* 7/12 + 5/10+5/12`

`1/(10*12)*(35+25)`

`60/(10*12) = 1/20`