Welcome! Check out our free B-School Guides to learn how you compare with other applicants.
Login or Register
 

Siblings

This topic has 2 expert replies and 5 member replies
Bookmark
Previous Topic Next Topic
neerajkumar1_1 Really wants to Beat The GMAT!
Joined
07 Apr 2010
Posted:
270 messages
Followed by:
1 members
Thanked:
21 times
Siblings Post Mon Sep 13, 2010 4:53 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    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

    This question has been answered before on the forum...
    but I cant understand the concept of siblings here...

    4 people have exactly 1 sibling means what... and 3 people have exactly 2 siblings means what...

    Plz explain... thanks...

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!

    GMAT/MBA Expert

    Jim@Grockit GMAT Instructor
    Joined
    22 Jul 2009
    Posted:
    643 messages
    Followed by:
    43 members
    Thanked:
    152 times
    GMAT Score:
    760
    Post Mon Sep 13, 2010 6:16 am
    neerajkumar1_1 wrote:
    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

    This question has been answered before on the forum...
    but I cant understand the concept of siblings here...

    4 people have exactly 1 sibling means what... and 3 people have exactly 2 siblings means what...

    Plz explain... thanks...
    "Siblings" means "brothers or sisters;" for simplicity's sake, consider replacing "sibling" in your head with "relative." It means that 4 people have one relative in the room, and 3 people have two relatives in the room. Does that help?

    neerajkumar1_1 Really wants to Beat The GMAT!
    Joined
    07 Apr 2010
    Posted:
    270 messages
    Followed by:
    1 members
    Thanked:
    21 times
    Post Mon Sep 13, 2010 6:23 am
    Jim@Grockit wrote:
    neerajkumar1_1 wrote:
    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

    This question has been answered before on the forum...
    but I cant understand the concept of siblings here...

    4 people have exactly 1 sibling means what... and 3 people have exactly 2 siblings means what...

    Plz explain... thanks...
    "Siblings" means "brothers or sisters;" for simplicity's sake, consider replacing "sibling" in your head with "relative." It means that 4 people have one relative in the room, and 3 people have two relatives in the room. Does that help?
    Well thats not the issue..
    I saw the solns...
    How does one sibling for 4 people relate to 2 pairs and so on for 3 people with 2 siblings...
    I am just getting thoroughly confused and am not able to visualize the problem...

    Hope u can provide me with a little more detail...

    neerajkumar1_1 Really wants to Beat The GMAT!
    Joined
    07 Apr 2010
    Posted:
    270 messages
    Followed by:
    1 members
    Thanked:
    21 times
    Post Tue Sep 14, 2010 3:54 am
    hi guyz... can someone plz provide me with a solution and including how we make the sets of siblings...

    kmittal82 GMAT Destroyer!
    Joined
    05 Jul 2010
    Posted:
    324 messages
    Followed by:
    3 members
    Thanked:
    67 times
    Target GMAT Score:
    720+
    Post Tue Sep 14, 2010 4:10 am
    >people have exactly 1 sibling

    Let them be A1 A2 B1 B2

    Siblings: A1-A2 and B1-B2

    >3 people have exactly 2 siblings in the room

    C1 C2 C3

    Siblings: C1-C2-C3

    To further simplify, you can say the people are A A B B C C C, but keep in mind when doing any selections, the order will matter (so use a permutation)

    neerajkumar1_1 Really wants to Beat The GMAT!
    Joined
    07 Apr 2010
    Posted:
    270 messages
    Followed by:
    1 members
    Thanked:
    21 times
    Post Tue Sep 14, 2010 4:14 am
    kmittal82 wrote:
    >people have exactly 1 sibling

    Let them be A1 A2 B1 B2

    Siblings: A1-A2 and B1-B2

    >3 people have exactly 2 siblings in the room

    C1 C2 C3

    Siblings: C1-C2-C3

    To further simplify, you can say the people are A A B B C C C, but keep in mind when doing any selections, the order will matter (so use a permutation)
    hi,
    In the fist set which u made..
    where it is given that 4 people have one sibling...

    how do u make 2 relations
    Siblings: A1-A2 and B1-B2

    I am just failing to interpret the question.. Sad

    GMAT/MBA Expert

    GMATGuruNY GMAT Instructor
    Joined
    25 May 2010
    Posted:
    6081 messages
    Followed by:
    1033 members
    Thanked:
    5239 times
    GMAT Score:
    790
    Most Active Expert Most Responsive Expert Most Thanked Expert
    Post Tue Sep 14, 2010 4:51 am
    neerajkumar1_1 wrote:
    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

    This question has been answered before on the forum...
    but I cant understand the concept of siblings here...

    4 people have exactly 1 sibling means what... and 3 people have exactly 2 siblings means what...

    Plz explain... thanks...
    Let's say that the 7 people are ABCDEFG.

    4 people have exactly 1 sibling:
    Let's say that A and B are siblings and that C and D are siblings.
    This means:
    A has 1 sibling (B).
    B has 1 sibling (A).
    C has 1 sibling (D).
    D has 1 sibling (C).

    3 people have exactly 2 siblings:
    Let's say that E, F and G are all siblings of each other.
    This means:
    E has 2 siblings (F and G).
    F has 2 siblings (E and G).
    G has 2 siblings (E and F).

    Total number of sibling pairs = 5: AB, CD, EF, EG, FG.
    Total number of pairs that can be formed from 7 people: 7C2 = 21.
    P(sibling pair) = 5/21
    P(not sibling pair) = 1 - 5/21 = 16/21.

    Does this help?

    _________________
    Mitch Hunt
    GMAT Private Tutor and Instructor
    GMATGuruNY@gmail.com
    If you find one of my posts helpful, please take a moment to click on the "Thank" icon.
    Contact me about long distance tutoring!

    Thanked by: neerajkumar1_1, singhsa, GmatKiss, tabsang, Fazze, rasha.dergham
    Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now.
    neerajkumar1_1 Really wants to Beat The GMAT!
    Joined
    07 Apr 2010
    Posted:
    270 messages
    Followed by:
    1 members
    Thanked:
    21 times
    Post Tue Sep 14, 2010 5:09 am
    GMATGuruNY wrote:
    neerajkumar1_1 wrote:
    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

    This question has been answered before on the forum...
    but I cant understand the concept of siblings here...

    4 people have exactly 1 sibling means what... and 3 people have exactly 2 siblings means what...

    Plz explain... thanks...
    Let's say that the 7 people are ABCDEFG.

    4 people have exactly 1 sibling:
    Let's say that A and B are siblings and that C and D are siblings.
    This means:
    A has 1 sibling (B).
    B has 1 sibling (A).
    C has 1 sibling (D).
    D has 1 sibling (C).

    3 people have exactly 2 siblings:
    Let's say that E, F and G are all siblings of each other.
    This means:
    E has 2 siblings (F and G).
    F has 2 siblings (E and G).
    G has 2 siblings (E and F).

    Total number of sibling pairs = 5: AB, CD, EF, EG, FG.
    Total number of pairs that can be formed from 7 people: 7C2 = 21.
    P(sibling pair) = 5/21
    P(not sibling pair) = 1 - 5/21 = 16/21.

    Does this help?
    it surely does... phew!!!!>.. I was like so frustrated...
    thanks a lot...

    Best Conversation Starters
    1 varun289 43 topics
    2 greenwich 30 topics
    3 sana.noor 22 topics
    4 guerrero 20 topics
    5 killerdrummer 18 topics
    See More Top Beat The GMAT Members...

    Most Active Experts
    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    		 205 posts
    2 image description Anju@Gurome

    Gurome

    		 146 posts
    3 image description GMATGuruNY

    The Princeton Review Teacher

    		 145 posts
    4 image description Jim@StratusPrep

    Stratus Prep

    		 96 posts
    5 image description David@VeritasPrep

    Veritas Prep

    		 39 posts
    See More Top Beat The GMAT Experts