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

remainder

This topic has 9 member replies
Bookmark
Previous Topic Next Topic
jainrahul1985 Really wants to Beat The GMAT! Default Avatar
Joined
17 Aug 2008
Posted:
228 messages
Thanked:
3 times
remainder Post Sat Jan 14, 2012 9:52 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    What is the remainder when 7 is divided by 10^548 ?
    A. 1 B. 3 C. 6 D. 7 E. 9
    OA A

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    rijul007 GMAT Destroyer!
    Joined
    16 Oct 2011
    Posted:
    588 messages
    Followed by:
    8 members
    Thanked:
    128 times
    Test Date:
    3rd May '12
    Target GMAT Score:
    750+
    GMAT Score:
    720
    Post Sat Jan 14, 2012 10:40 am
    are you sure the ques is correct??

    I am getting 2 as the ans...

    ronnie1985 GMAT Destroyer!
    Joined
    23 Dec 2011
    Posted:
    626 messages
    Followed by:
    9 members
    Thanked:
    29 times
    Test Date:
    June
    Target GMAT Score:
    750
    Post Sat Jan 14, 2012 11:44 am
    Please read the question carefully. It asks what is the remainder when [b][u]7 is divided by 10^something, which is greater than 7 and hence remainder will be 7 only (D). If the question had been what's the remainder when 10^548 is divide by 7 then
    Consider R(x/y) = z means remainder when x is divided by y is equal to z
    R(10^548/7)=R(3^548/7)=R(9^274/7)=R(8^91x2/7)=R(1x2/7)=R(2/7)=2
    Hence 2 is the remainder in that case which is not given in the options.

    _________________
    Follow your passion, Success as perceived by others shall follow you

    ArunangsuSahu GMAT Destroyer! Default Avatar
    Joined
    31 Mar 2011
    Posted:
    383 messages
    Thanked:
    14 times
    Post Sat Jan 14, 2012 12:09 pm
    (D)

    if 10^548/7 then 2

    gmatpup Rising GMAT Star Default Avatar
    Joined
    15 Oct 2011
    Posted:
    88 messages
    Thanked:
    1 times
    Post Tue Jan 17, 2012 10:00 am
    Normally when I am faced with a remainder question I break the larger number down into its primes.. In this case it would be 137 (because I break down the 548) so I am getting a remainder of 0.05

    guha.santanu@gmail.com Rising GMAT Star Default Avatar
    Joined
    21 Dec 2009
    Posted:
    57 messages
    Thanked:
    17 times
    Target GMAT Score:
    730
    Post Tue Jan 17, 2012 6:53 pm
    ronnie1985 wrote:
    Please read the question carefully. It asks what is the remainder when [b][u]7 is divided by 10^something, which is greater than 7 and hence remainder will be 7 only (D). If the question had been what's the remainder when 10^548 is divide by 7 then
    Consider R(x/y) = z means remainder when x is divided by y is equal to z
    R(10^548/7)=R(3^548/7)=R(9^274/7)=R(8^91x2/7)=R(1x2/7)=R(2/7)=2
    Hence 2 is the remainder in that case which is not given in the options.
    Could you please explain how you have derived R(9^274/7)=R(8^91x2/7)=R(1x2/7)?

    ronnie1985 GMAT Destroyer!
    Joined
    23 Dec 2011
    Posted:
    626 messages
    Followed by:
    9 members
    Thanked:
    29 times
    Test Date:
    June
    Target GMAT Score:
    750
    Post Wed Jan 18, 2012 1:17 am
    guha.santanu@gmail.com wrote:
    ronnie1985 wrote:
    Please read the question carefully. It asks what is the remainder when [b][u]7 is divided by 10^something, which is greater than 7 and hence remainder will be 7 only (D). If the question had been what's the remainder when 10^548 is divide by 7 then
    Consider R(x/y) = z means remainder when x is divided by y is equal to z
    R(10^548/7)=R(3^548/7)=R(9^274/7)=R(8^91x2/7)=R(1x2/7)=R(2/7)=2
    Hence 2 is the remainder in that case which is not given in the options.
    Could you please explain how you have derived R(9^274/7)=R(8^91x2/7)=R(1x2/7)?
    3^548 = (3^2*274) = 9^274

    _________________
    Follow your passion, Success as perceived by others shall follow you

    ronnie1985 GMAT Destroyer!
    Joined
    23 Dec 2011
    Posted:
    626 messages
    Followed by:
    9 members
    Thanked:
    29 times
    Test Date:
    June
    Target GMAT Score:
    750
    Post Wed Jan 18, 2012 1:24 am
    ronnie1985 wrote:
    guha.santanu@gmail.com wrote:
    ronnie1985 wrote:
    Please read the question carefully. It asks what is the remainder when [b][u]7 is divided by 10^something, which is greater than 7 and hence remainder will be 7 only (D). If the question had been what's the remainder when 10^548 is divide by 7 then
    Consider R(x/y) = z means remainder when x is divided by y is equal to z
    R(10^548/7)=R(3^548/7)=R(9^274/7)=R(8^91x2/7)=R(1x2/7)=R(2/7)=2
    Hence 2 is the remainder in that case which is not given in the options.
    Could you please explain how you have derived R(9^274/7)=R(8^91x2/7)=R(1x2/7)?
    3^548 = (3^2*274) = 9^274
    Also when 9 is divided by 7 remainder is 2
    so R(9^274/7) = R(2^274/7)
    Please note that 2^273 = 2^3*91=8^91
    2^274 = (8^91)*2
    therefore, R(2^274/7) = R(((8^91)*2)/7)
    Also note 8 divided by 7 leaves 1 as remainder.
    Therefore remainder R(((8^91)*2)/7) = R(1*2/7) = 2

    I hope now it is easy to undersdtand

    _________________
    Follow your passion, Success as perceived by others shall follow you

    guha.santanu@gmail.com Rising GMAT Star Default Avatar
    Joined
    21 Dec 2009
    Posted:
    57 messages
    Thanked:
    17 times
    Target GMAT Score:
    730
    Post Wed Jan 18, 2012 2:44 am
    Initially I didn't understand the part "Also when 9 is divided by 7 remainder is 2 so R(9^274/7) = R(2^274/7) "
    Thanks mate!

    abby17 Just gettin' started! Default Avatar
    Joined
    20 Jan 2012
    Posted:
    17 messages
    Target GMAT Score:
    760+
    Post Fri Jan 20, 2012 11:19 pm
    I assume the question is 10^548/7

    Since 7 and 10 are co-prime, divide the given power (548) by 6(one less than the divisor). This division gives 2 as the remainder.
    So the question now reduces to what is the remainder when 10^2 is divided by 7.
    Now this is very easy to solve. 100/7 gives 2 as the remainder.

    Hope this helps.

    Best Conversation Starters
    1 varun289 42 topics
    2 greenwich 25 topics
    3 guerrero 20 topics
    4 sana.noor 19 topics
    5 killerdrummer 19 topics
    See More Top Beat The GMAT Members...

    Most Active Experts
    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    		 196 posts
    2 image description GMATGuruNY

    The Princeton Review Teacher

    		 143 posts
    3 image description Anju@Gurome

    Gurome

    		 121 posts
    4 image description Jim@StratusPrep

    Stratus Prep

    		 86 posts
    5 image description David@VeritasPrep

    Veritas Prep

    		 41 posts
    See More Top Beat The GMAT Experts