Siblings

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adam15: Senior | Next Rank: 100 Posts; Posts: 70; Joined: Mon May 12, 2008 12:26 pm; Thanked: 3 times

by adam15 » Wed Nov 25, 2009 2:04 pm

In a room filled with 7 people, 4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. If two individuals are selected from the room at random, what is the probability that those two individuals are NOT siblings?
5/21
3/7
4/7
5/7
16/21

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Source: Beat The GMAT — Problem Solving | Wed Nov 25, 2009 2:04 pm

capnx: Master | Next Rank: 500 Posts; Posts: 268; Joined: Sat Aug 15, 2009 9:22 amFollowed by: 1 member; Thanked: 19 times; GMAT Score:700

by capnx » Wed Nov 25, 2009 3:42 pm

great explanation here:
https://www.beatthegmat.com/probability-t48338.html

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