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OG Quant Review: DS, Chapter 5.5, Problem 117 wrong?

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gmatace Newbie | Next Rank: 10 Posts Default Avatar
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OG Quant Review: DS, Chapter 5.5, Problem 117 wrong?

Post Fri Apr 14, 2006 9:35 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Has anyone see this happen?

    I think their answer is wrong..

    They have a triangle ABC, And a point D on AC. BDC = BCD = 2xdegree.
    What is BC?

    1) AD = 6
    2) x = 36

    They say AD = 6 is sufficient to know the length of BC.
    I dont think so.. We know BD = BC, because angles are equal.. but I dont know how do they conclude AD = BD from this? Please help..

    Has anyone else seen this?

    Attaching the file..
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    dkiran01 Junior | Next Rank: 30 Posts Default Avatar
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    Post Sun Apr 16, 2006 12:02 am
    i think the answer is wrong.. how can it be A Rolling Eyes

    humblewinner Newbie | Next Rank: 10 Posts Default Avatar
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    Post Tue May 02, 2006 10:58 am
    Yes, It looks wrong.

    aim-wsc Legendary Member
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    Post Thu May 18, 2006 3:51 pm
    looks like a printing error.

    answer should be E. Crying or Very sad

    lan0583 Junior | Next Rank: 30 Posts Default Avatar
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    Post Sun May 21, 2006 5:37 pm
    the problem is correct and the answer is E.

    For the first one, the problem didnt say that AD is equal to DC. So it doesnt matter whether AD has a value.

    For the second, you cant get the answer for if theres no value. the problem gave the value of x, and x is the degree not the length.

    aim-wsc Legendary Member
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    Post Mon May 22, 2006 1:02 am
    @lan0583

    if u r saying that answer is E on which we all r agree.

    then problem cannot be correct.

    i mean problem is correct but the answer given (ie A ) is incorrect.

    lan0583 Junior | Next Rank: 30 Posts Default Avatar
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    Post Tue May 23, 2006 6:18 am
    the problem is correct. the answer is not

    Post Fri Jun 02, 2006 10:00 pm
    Hi All,
    I have seen this problem before (I dont remeber the OG guide version). I remember that the angle BAC is "x" degrees.

    This info in addition to the what gmatace posted helps us solve this problem.

    Try it out. Hope this is helpful Smile

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    Fei Junior | Next Rank: 30 Posts Default Avatar
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    Post Wed Jun 14, 2006 12:42 am
    No. the book's answer is correct. I think the answer in the book explains this question sufficiently using the rule that, " the degree measure of an exterior angle of a triangle is equal to the sum of the remote interior angles"

    therefore, according to this rule, BDC is then an exterior angle of triangle ADB and equal to its remote interior angles which are angles ABD ( call this x) and DAB ( call this y). Therefore x+y=2x, therefore you know y=x, and you can go from here. this is all in the solution that the OG gives. Statement 1 only is sufficient. Hope this helps.

    I am disappointed in the theory coverage of the OG though, as they are using geometry rules including mini arcs, rules such as the one above where I have not seen coverage anywhere... I am really glad that I am learning these new rules as I go along as they are simply not covered in the KAPlan, Princeton or any OG books.

    jbsears Newbie | Next Rank: 10 Posts Default Avatar
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    Post Sat Jun 24, 2006 10:11 pm
    The answer of this question is wrong. It should be E.

    If you think the explanation is right, you are making an assumption that can't be made which is the same mistake the OG made. One can't assume one of the angles equals x. instead of x+y=2x it should be z+y=2x. If you can't understand this then draw a few example that cannot possibly follow reasoning of the OG. That's what I did to validate my assumptions about OG's mistake.

    aim-wsc Legendary Member
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    Post Mon Jun 26, 2006 12:31 am
    hi jbsears,
    did u follow what mr. Rahul said?
    BAC is x.
    that solves all problem. the q published & file uploaded here on d web site therefore must have been incorrect.
    with Rahuls INFO ans. is A.
    agree with FEI:)

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    jbsears Newbie | Next Rank: 10 Posts Default Avatar
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    Post Mon Jun 26, 2006 2:02 am
    aim-wsc,

    Rahul's answer is right if that is true but it is not. The OG doesn't give the angle BAC is X. Therefore, one cannot assume it is X. Maybe there are alternative versions of the book, but the book I have doesn't have BAC listed as X. So the answer is E. But if it was X, then A would be the correct answer.

    diabl020 Newbie | Next Rank: 10 Posts Default Avatar
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    Post Sat Jan 20, 2007 6:18 am
    phew... glad I found this.. I was going cross-eyed reading the explanation in the OG which wasn't making any sense to me..

    They've missed a vital bit of information while printing it... It must be stated that BAC is x, or half of BDC, or something.

    It's kinda dissappointing actually.. Giving 'sufficient' data is most critical in the Data Sufficiency section..

    jineu Newbie | Next Rank: 10 Posts Default Avatar
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    Post Mon Apr 02, 2007 6:36 am
    There is a same question in OG10 with extra information. With the information given in OG 10, the correct answer is absolutely A, but without it, the correct answer is E.

    RAGS Senior | Next Rank: 100 Posts Default Avatar
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    Post Thu Apr 12, 2007 9:52 am
    can somebody explain how by giving /BAD as X we can get the ans with A alone???????????

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