GMAT Prep Day 18

Posted: July 10th, 2006 | Author: Jeff | Filed under: Uncategorized | 7 Comments »

Finished GMAC Challenge #2.  Seemed a lot easier than Challenge #1.  Perhaps I rushed through Challenge #1 and made a lot of careless errors (or just wasn’t as cognizant of the ’traps’ during the first challenge).  Mindmapped the tough questions and reviewed the explanations.  Here was the toughest problem I came across (actually got it right!).  See if you can solve it under 2 minutes:

There are four distinct pairs of brothers and sisters.  In how many ways can a committee of 3 be formed and not have siblings in it?

A) 8   B) 24   C) 32  D) 56  E) 80

I’ll be doing 5 challenges per week and 1-2 practice tests a week on average.  Bought Franklin Covey PlanPlus for Outlook v.3 that will help me stay on top of things (Outlook Inbox, Tasks, Calendar, Notes in one view!). 

7 Comments on “GMAT Prep Day 18”

  1. 1 jimmy said at 10:49 am on July 11th, 2006:

    i know that the answer will be 32 but i do not know the direct solution .if anybody has the solution to this problem plz post it to me on my mail acoount jim_…@yahoomail.com

  2. 2 jimmy said at 10:55 am on July 11th, 2006:

    sorry i just figured out the solution to the problem.
    it goes lioke this 8 C 3 -24 .24 IS TAKEN BECAUSE EACH PAIR WILL HAVE 6 COMBINATIONS WITH EACH OTHER

  3. 3 Allan said at 10:10 pm on July 11th, 2006:

    I’m going to guess 80 with about 30 seconds of trying to figure it out. Any luck?

  4. 4 Allan said at 10:16 pm on July 11th, 2006:

    I nearly came back and second guess myself just now but now I’m fairly confident of my answer.

  5. 5 Allan said at 9:46 pm on July 12th, 2006:

    Man, I’m dyin’ here.

  6. 6 Administrator said at 1:52 am on July 13th, 2006:

    Answer: C

    Here, we want to find the total outcomes and subtract the unfavorable outcomes, leaving us with favorable outcomes only.

    Total # of groups of 3 out of 8 people is 8!/(3!5!) = 56. Unfavorable outcomes = 4*C(6,1) = 24. (when choose one pair of siblings, 6 people left; multiply by 4 becuse there are 4 pairs). THe difference between total and unfavorable outcomes = favorable outcomes = 56-24 = 32.

  7. 7 Allan said at 8:46 pm on July 13th, 2006:

    omg, I don’t read carefully.

    I for some reason started thinking about how many combinations of four people without siblings.

    Damn ADD.

    Keep posting those, they’re fun.

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