• Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep

If A, then B. If B, then C....

This topic has 9 member replies
figs Senior | Next Rank: 100 Posts Default Avatar
Joined
30 Mar 2009
Posted:
70 messages
Thanked:
2 times
Test Date:
28/06/2009

If A, then B. If B, then C....

Post Tue May 19, 2009 12:34 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    If A, then B.
    If B, then C.
    If C, then D.

    If all of the statements above are true, which of the following must also be true?
    A. If D, then A
    B. If not B, then not C
    C. If not D, then not A
    D. If D, then E
    E. If not A, then not D

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    vinaynp Master | Next Rank: 500 Posts Default Avatar
    Joined
    19 Mar 2009
    Posted:
    154 messages
    Followed by:
    1 members
    Thanked:
    5 times
    Post Tue May 19, 2009 3:00 pm
    figs wrote:
    If A, then B.
    If B, then C.
    If C, then D.

    If all of the statements above are true, which of the following must also be true?
    A. If D, then A
    B. If not B, then not C
    C. If not D, then not A
    D. If D, then E
    E. If not A, then not D
    I would like to think of all the three statements independent and represent below:

    A->B
    B->C
    C->D

    A) It cannot be true.
    C) It cannot be true.
    D) Out of scope.
    E) It cannot be true.
    B) If not B then not C is true.

    The answer is B.

    rahulg83 Legendary Member
    Joined
    04 Nov 2008
    Posted:
    575 messages
    Followed by:
    4 members
    Thanked:
    18 times
    Test Date:
    09-Jul-2009
    GMAT Score:
    710
    Post Tue May 19, 2009 7:02 pm
    IMO B

    scoobydooby Legendary Member Default Avatar
    Joined
    27 Aug 2008
    Posted:
    1035 messages
    Followed by:
    1 members
    Thanked:
    104 times
    Post Tue May 19, 2009 11:50 pm
    would go for C

    If A, then B.
    If B, then C.
    If C, then D

    =>if A then D
    =>if not D, then not A

    thetrystero Master | Next Rank: 500 Posts Default Avatar
    Joined
    13 Apr 2009
    Posted:
    154 messages
    Thanked:
    3 times
    Post Wed May 20, 2009 12:01 am
    figs wrote:
    If A, then B.
    If B, then C.
    If C, then D.

    If all of the statements above are true, which of the following must also be true?
    A. If D, then A
    B. If not B, then not C
    C. If not D, then not A
    D. If D, then E
    E. If not A, then not D
    My answer: None of the above.

    B sounds like a plausible choice at first, but not B doesn't necessarily imply not C.
    If it rains tomorrow, I will have hot chocolate.
    If it doesn't rain tomorrow, I will also have hot chocolate (or I may not).

    KICKGMATASS123 Master | Next Rank: 500 Posts Default Avatar
    Joined
    26 Feb 2009
    Posted:
    113 messages
    Test Date:
    June 10, 2009
    Target GMAT Score:
    700+
    GMAT Score:
    650
    Post Sun May 24, 2009 6:25 pm
    figs wrote:
    If A, then B.
    If B, then C.
    If C, then D.

    If all of the statements above are true, which of the following must also be true?
    A. If D, then A
    B. If not B, then not C
    C. If not D, then not A
    D. If D, then E
    E. If not A, then not D
    Figs can you post the OA pls?

    vinaynp Master | Next Rank: 500 Posts Default Avatar
    Joined
    19 Mar 2009
    Posted:
    154 messages
    Followed by:
    1 members
    Thanked:
    5 times
    Post Sun May 24, 2009 8:20 pm
    KICKGMATASS123 wrote:
    figs wrote:
    If A, then B.
    If B, then C.
    If C, then D.

    If all of the statements above are true, which of the following must also be true?
    A. If D, then A
    B. If not B, then not C
    C. If not D, then not A
    D. If D, then E
    E. If not A, then not D
    Figs can you post the OA pls?
    The OA is C

    This is a logic problem and we shouldn't be expecting this as part of the GMAT. I am going to show how we can get it from truth table.

    (-> is then) From the given information, we can conclude that A->D is true. I will construct the truth table using http://en.wikipedia.org/wiki/Truth_table#Logical_implication
    T= TRUE
    F=FALSE

    Please look at the file attached.

    A->D and ~D->~A have the same truth table and hence is the right answer.
    Attachments

    This post contains an attachment. You must be logged in to download/view this file. Please login or register as a user.

    Domnu Master | Next Rank: 500 Posts
    Joined
    24 May 2009
    Posted:
    385 messages
    Thanked:
    11 times
    Test Date:
    2011. Practicing now
    Target GMAT Score:
    800
    GMAT Score:
    740
    Post Thu May 28, 2009 9:16 am
    Another (slightly simplified) way of seeing this is as follows:

    A implies B
    B implies C
    C implies D

    all together imply that A implies D. By the contrapositive (not converse!), we have that not D implies not A. Generally, for ALL statements, if A implies B, then "not B" implies " not A".

    For example, if you're a human, you have a brain. If you don't have a brain, you're not a human.

    _________________
    Have you wondered how you could have found such a treasure? -T

    james33 Master | Next Rank: 500 Posts Default Avatar
    Joined
    22 Aug 2015
    Posted:
    200 messages
    Post Sun May 15, 2016 7:43 pm
    Cannot decide between A and B. Can anyone brake down these two choices for me please

    soudeh Junior | Next Rank: 30 Posts
    Joined
    20 Apr 2017
    Posted:
    20 messages
    Post Mon Sep 11, 2017 2:45 pm
    Hello


    would you explain more?

    I thought in this way:

    a: staying hungry
    b: getting sick
    c: leaving work
    d: no money!

    then if A doesn't happen, D will not happen
    but D can happen independently
    am I wrong??

    Best Conversation Starters

    1 Vincen 132 topics
    2 lheiannie07 69 topics
    3 LUANDATO 61 topics
    4 Roland2rule 42 topics
    5 ardz24 40 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    134 posts
    2 image description EconomistGMATTutor

    The Economist GMAT Tutor

    117 posts
    3 image description GMATGuruNY

    The Princeton Review Teacher

    117 posts
    4 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    109 posts
    5 image description DavidG@VeritasPrep

    Veritas Prep

    76 posts
    See More Top Beat The GMAT Experts