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

multiples of 7

This topic has 2 expert replies and 3 member replies
j_shreyans GMAT Destroyer! Default Avatar
Joined
07 Aug 2014
Posted:
510 messages
Followed by:
5 members
Thanked:
3 times
multiples of 7 Post Mon Sep 08, 2014 10:17 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    What is the sum of the multiples of 7 from 84 to 140, inclusive?

    A)896
    B)963
    c)1008
    D)1792
    E)2016

    OAC

    How to approach this kind of question?

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    abhasjha GMAT Destroyer! Default Avatar
    Joined
    30 Sep 2008
    Posted:
    379 messages
    Followed by:
    11 members
    Thanked:
    28 times
    Post Mon Sep 08, 2014 10:27 pm
    This question tests your knoweldge of AP series

    84 = 12x7 .. so 84 is 12the term
    140= 20 X7 ..... 140 is 20th term ....

    so total number of terms between 84 and 140 = 9 . ( using the formula total numbers between b and a inclusisve is( b-a ) +1

    now the sum of an AP series is... n/2 ( first term + last Term ) = 9/2 (84 +140 ) = 1008

    Answer C .

    Post Mon Sep 08, 2014 10:30 pm
    j_shreyans wrote:
    What is the sum of the multiples of 7 from 84 to 140, inclusive?

    A)896
    B)963
    c)1008
    D)1792
    E)2016

    In other words, 84 + 91 + 98 + . . . 140 = ?

    Since the values are EQUALLY SPACED, we can use the rule: SUM = [(FIRST + LAST)/2][# of values]

    NUMBER of values
    Here's a nice rule: If x and y are multiples of k, then the number of multiples of k from x to y inclusive = [(y-x)/k] + 1
    So, for example, the NUMBER multiples of 3 from 6 to 21 inclusive = [(21 - 6)/3] + 1 = [15/3] + 1 = 6

    So, the NUMBER multiples of 7 from 84 to 140 inclusive = [(140 - 84)/7] + 1
    = [56/7] + 1
    = 9

    ------------------------------------

    Now apply the formula:
    SUM = [(FIRST + LAST)/2][# of values]
    = [(84 + 140)/2][9]
    = [224/2][9]
    = [112][9]
    = 1008
    = C

    Cheers,
    Brent

    _________________
    Brent Hanneson – Founder of GMATPrepNow.com
    Use our video course along with Beat The GMAT's free 60-Day Study Guide

    Enter our contest to win a free course.



    Last edited by Brent@GMATPrepNow on Fri Feb 12, 2016 8:13 pm; edited 1 time in total

    Thanked by: manik11
    GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!
    prada Rising GMAT Star Default Avatar
    Joined
    08 Dec 2010
    Posted:
    59 messages
    Thanked:
    1 times
    Post Fri Feb 12, 2016 4:06 pm
    Brent@GMATPrepNow wrote:
    j_shreyans wrote:
    What is the sum of the multiples of 7 from 84 to 140, inclusive?

    A)896
    B)963
    c)1008
    D)1792
    E)2016

    In other words, 84 + 91 + 98 + . . . 140 = ?

    Since the values are EQUALLY SPACED, we can use the rule: SUM = [(FIRST + LAST)/2][# of values]

    NUMBER of values
    Here's a nice rule: If x and y are multiples of k, then the number of multiples of k from x to y inclusive = [(y-x)/k] + 1
    So, for example, the NUMBER multiples of 3 from 6 to 21 inclusive = [(21 - 6)/3] + 1 = [15/3] + 1 = 6

    So, the NUMBER multiples of 7 from 84 to 140 inclusive = [(140 - 84)/3] + 1
    = [56/7] + 1
    = 9

    ------------------------------------

    Now apply the formula:
    SUM = [(FIRST + LAST)/2][# of values]
    = [(84 + 140)/2][9]
    = [224/2][9]
    = [112][9]
    = 1008
    = C

    Cheers,
    Brent
    Hi Brent,

    I think here
    So, the NUMBER multiples of 7 from 84 to 140 inclusive = [(140 - 84)/3] + 1

    you mean 7 in lieu of 3?

    Thanked by: Brent@GMATPrepNow
    Post Fri Feb 12, 2016 8:14 pm
    prada wrote:
    you mean 7 in lieu of 3?
    You're absolutely right. Good catch.
    I edited my response accordingly.

    Cheers,
    Brent

    _________________
    Brent Hanneson – Founder of GMATPrepNow.com
    Use our video course along with Beat The GMAT's free 60-Day Study Guide

    Enter our contest to win a free course.

    GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!
    waleedijaz Just gettin' started! Default Avatar
    Joined
    30 Apr 2016
    Posted:
    1 messages
    Post Sat Apr 30, 2016 4:07 am
    You're absolutely right. Good catch???


    waleeed

    Best Conversation Starters

    1 aditiniyer 21 topics
    2 Mo2men 15 topics
    3 rsarashi 11 topics
    4 neha shekhawat 8 topics
    5 neeti2711 7 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    113 posts
    2 image description GMATGuruNY

    The Princeton Review Teacher

    105 posts
    3 image description Matt@VeritasPrep

    Veritas Prep

    81 posts
    4 image description DavidG@VeritasPrep

    Veritas Prep

    77 posts
    5 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    73 posts
    See More Top Beat The GMAT Experts