Question

A box contains four blue and eight red balls. Jim and Jack start drawing balls from the box, respectively, one at a time, at random, and without replacement until a blue ball is drawn. What is the probability that Jack draws the blue ball?

Answer 1

the probability that Jack draws the blue ball is 0.38539

Explanation:

Given the data in the question;

box contains

blue balls = 5

red balls = 8

Jim and Jack start drawing balls from the box, respectively, one at a time, at random, and without replacement

Now,

on the first attempted;

⇒ ( 8/13) × ( 5/12) = 10/39

on the second attempt;

⇒ ( 8/13 ) ( 7/12) ( 6/11 ) ( 5/10 ) = 14/143

on the third attempt;

⇒ ( 8/13 ) ( 7/12) ( 6/11 ) ( 5/10 ) ( 4/9 ) ( 5/8 ) = 35/1287

on the fourth attempt;

⇒ ( 8/13 ) ( 7/12) ( 6/11 ) ( 5/10 ) ( 4/9 ) ( 3/8 ) ( 2/7 ) ( 5/6 ) = 5/1287

so we add everything;

⇒ 10/39 + 14/143 + 35/1287 + 5/1287

= 0.38539

Therefore, the probability that Jack draws the blue ball is 0.38539