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

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • 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

OG12 #70 - value of n? Why isnt n =0 ??

This topic has 1 expert reply and 3 member replies
rohit_gmat Master | Next Rank: 500 Posts
Joined
16 Jun 2010
Posted:
158 messages
Followed by:
1 members
Thanked:
13 times

OG12 #70 - value of n? Why isnt n =0 ??

Post Sun Oct 10, 2010 7:32 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Mary persuaded n friends to donate $500 each to her election campaign, and each of those n friends persuaded n more friends to donate $500 each to Mary's campaign. If no one donated more than once and if there were no other donations, what was the value of n?
    (1) The first n people donated 1/16 of the total amount donated
    (2) The total amount donated was $120,000.

    The OA is D

    But I thought B was the correct answer.
    With both statments we get quadratic equations :
    Statement 1 gives us : n =0 or 15
    Statement 2 gives us : n = -16 or 15 (this is clear since -16 people is not possible, so 15 must be the value)
    But GMAC says - "Assuming n>0" statement 1 gives us n = 15....... WHY CAN'T n = 0 ??
    When can we assume in the GMAT that n>0?? And when can we not?? i.e. when the question doesn't clearly specify...

    [/b]

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    selango Legendary Member
    Joined
    29 Dec 2009
    Posted:
    1460 messages
    Followed by:
    7 members
    Thanked:
    135 times
    Post Sun Oct 10, 2010 8:02 am
    rohit bro,

    You mentioned that in stmt2 that n=-16 is not possible..then how come n=0 also possible?It means there are 0 number of friends (or) no friends at all(or) in this case no question at all unless the total amount is zero.
    Here n represents number of friends.So we need to assume that n>0.

    PS:By the way u think the question ll be stated in this way huh?


    Mary persuaded n friends to donate $500 each to her election campaign, and each of those n friends persuaded n more friends to donate $500 each to Mary's campaign. If no one donated more than once and if there were no other donations, what was the value of n?
    Note that n is an positive integer since it represent the number of friends.

    Just Kidding yaar Mr. Green

    _________________
    --Anand--

    rohit_gmat Master | Next Rank: 500 Posts
    Joined
    16 Jun 2010
    Posted:
    158 messages
    Followed by:
    1 members
    Thanked:
    13 times
    Post Sun Oct 10, 2010 7:39 pm
    Hi Selango,

    Im genuinely in doubt man!... I assumed n not equal to -16 since negative 16 is not a possible number of friends (or people)... but zero is... isnt it? ... Mary was probably a loser and had no friends who gave no money...??

    Actually, after posting this I saw a post from another guy with a similar issue... and a GMAT guru advised that in the GMAT for real life problems, the trick is never "assuming 0".... theres another question in the OG abt 2 cities' populations and their leaders or smth like tht... and if one assumes that population is zero then the question goes crazy...

    thanks for ur support anyway Razz

    Viktri Junior | Next Rank: 30 Posts Default Avatar
    Joined
    12 Aug 2010
    Posted:
    12 messages
    Post Wed Oct 13, 2010 9:26 pm
    Data given:

    n x 500 + n x n x 500
    total = 1500n

    i) (n+500) x 16 = 1500n
    solvable

    ii) 1500n = 120,000
    solvable



    rohit_gmat wrote:
    Mary persuaded n friends to donate $500 each to her election campaign, and each of those n friends persuaded n more friends to donate $500 each to Mary's campaign. If no one donated more than once and if there were no other donations, what was the value of n?
    (1) The first n people donated 1/16 of the total amount donated
    (2) The total amount donated was $120,000.

    The OA is D

    But I thought B was the correct answer.
    With both statments we get quadratic equations :
    Statement 1 gives us : n =0 or 15
    Statement 2 gives us : n = -16 or 15 (this is clear since -16 people is not possible, so 15 must be the value)
    But GMAC says - "Assuming n>0" statement 1 gives us n = 15....... WHY CAN'T n = 0 ??
    When can we assume in the GMAT that n>0?? And when can we not?? i.e. when the question doesn't clearly specify...

    [/b]

    GMAT/MBA Expert

    Testluv GMAT Instructor Default Avatar
    Joined
    19 Oct 2009
    Posted:
    1302 messages
    Followed by:
    162 members
    Thanked:
    538 times
    GMAT Score:
    800
    Post Wed Oct 13, 2010 9:48 pm
    selango wrote:
    rohit bro,

    PS:By the way u think the question ll be stated in this way huh?


    Mary persuaded n friends to donate $500 each to her election campaign, and each of those n friends persuaded n more friends to donate $500 each to Mary's campaign. If no one donated more than once and if there were no other donations, what was the value of n?
    Note that n is an positive integer since it represent the number of friends.

    Just Kidding yaar Mr. Green
    ...hilarious.

    In PS word problems that describe a situation, you can always assume that the number of entities is such that the situation exists (this usually means that they are all positive integers.) Or as selango points out, if we let n = 0, then Mary has no friends, and there is no question at all (because the situation wouldn't exist).

    _________________
    Kaplan Teacher in Toronto

    Free GMAT Practice Test under Proctored Conditions! - Find a practice test near you or live and online in Kaplan's Classroom Anywhere environment. Register today!

    Best Conversation Starters

    1 Vincen 152 topics
    2 lheiannie07 61 topics
    3 Roland2rule 49 topics
    4 ardz24 40 topics
    5 LUANDATO 32 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    141 posts
    2 image description EconomistGMATTutor

    The Economist GMAT Tutor

    107 posts
    3 image description GMATGuruNY

    The Princeton Review Teacher

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

    EMPOWERgmat

    104 posts
    5 image description Matt@VeritasPrep

    Veritas Prep

    76 posts
    See More Top Beat The GMAT Experts