probability

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sharmishtha_goel: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Thu Feb 17, 2011 9:13 am; Thanked: 1 times

by sharmishtha_goel » Fri Jul 29, 2011 12:09 pm

25. A box contains 3 yellow 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?
1/4

1/2
5/8
2/3
3/4

the answer is 5/8. My doubt is that it asks probability of 4th ball being black so why should we not consider the following cases where the 4th ball is black

YYYB
YYBB
YBBB
BBBB

TIA.

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Source: Beat The GMAT — Problem Solving | Fri Jul 29, 2011 12:09 pm

Bek: Senior | Next Rank: 100 Posts; Posts: 68; Joined: Fri Dec 03, 2010 10:29 pmFollowed by: 1 member; Thanked: 5 times

by Bek » Fri Jul 29, 2011 8:43 pm

LOOK HERE:

https://www.beatthegmat.com/probablity-ques-t60161.html

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