In this task, you need to provide the correct option for a given problem on probability from the provided options.
One example is below.
Q: Problem: in a throw of a coin find the probability of getting a tail ? 
Options: a ) 1 / 2 , b ) 1 / 3 , c ) 1 / 4 , d ) 2 / 5 , e ) 2 / 7
A: a
Rationale: "s = { h , t } e = { t } p ( e ) = 1 / 2 answer is a"
Q: Problem: a box contains 2 red balls and 5 black balls . one by one , every ball is selected at random without replacement . what is the probability that the fourth ball selected is black ? 
Options: a ) 1 / 4 , b ) 7 / 5 , c ) 1 / 2 , d ) 5 / 8 , e ) 2 / 3
A:
b