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

Fraction Cancellation Rules

This topic has 1 expert reply and 4 member replies
stevennu Rising GMAT Star Default Avatar
Joined
18 May 2013
Posted:
54 messages
Followed by:
1 members
Fraction Cancellation Rules Post Sun Aug 04, 2013 4:42 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    I'm working through the Manhattan GMAT quant books and came across the following question.

    Simplify: 10X / 5 + X

    Why can't we simplify by cancelation? I know there are rules that regulate when we can and cannot cancel but I cannot seem to find a concise set of rules anywhere. Can someone shed some light?

    Thanks

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    Post Mon Aug 05, 2013 12:08 am
    Hi stevennu,

    What you've typed in your post needs some clarification.

    The fraction that you want to simplify...is it this:

    10X/5 + X

    or is it this:

    10X / (5 + X)

    GMAT assassins aren't born, they're made,
    Rich

    stevennu Rising GMAT Star Default Avatar
    Joined
    18 May 2013
    Posted:
    54 messages
    Followed by:
    1 members
    Post Mon Aug 05, 2013 11:24 am
    The latter.

    10X/(5+X)

    stevennu Rising GMAT Star Default Avatar
    Joined
    18 May 2013
    Posted:
    54 messages
    Followed by:
    1 members
    Post Mon Aug 05, 2013 11:53 am
    I think the following link pretty much spells out the rule I was looking for.

    That is, you cannot reduce part of a sum or part of a difference. Can you provide me any other links or examples?

    http://www.regentsprep.org/Regents/math/ALGEBRA/AV5/reducefrac.htm

    Thanks.

    GMAT/MBA Expert

    Matt@VeritasPrep GMAT Instructor
    Joined
    12 Sep 2012
    Posted:
    385 messages
    Followed by:
    47 members
    Thanked:
    163 times
    Target GMAT Score:
    V51
    GMAT Score:
    780
    Most Active Expert Most Responsive Expert Most Thanked Expert
    Post Mon Aug 05, 2013 6:44 pm
    One way of thinking about it:

    (10X + 8)/2 = (10X)/2 + 8/2 = 5x + 4

    Since you can break the sum into two fractions, you can break them up, then reduce each one individually.

    But (10X)/(8+2) is NOT (10x)/8 + (10x)/2, or (5/4)x + 5x ... it's (10X)/10, or x.

    So you CAN'T break these up into two fractions and reduce each part individually.

    As for fraction rules, how about:

    http://isites.harvard.edu/fs/docs/icb.topic760749.files/webAPPEodd.pdf

    _________________
    Join me every week on BTG for GMATT Mondays: an hour of live math and verbal Q&A. Drop by and stump me!

    http://www.veritasprep.com/g-matt-mondays/

    Drop me a thanks if you liked my posts (and two if you didn't!)

    Get 7 Veritas Prep GMAT Practice Tests for Just $24! Veritas Prep’s computer-adaptive GMAT practice test are powered by artificial intelligence, guaranteeing that you see the most realistic GMAT questions and most accurate scores. Get Your Tests Now.
    stevennu Rising GMAT Star Default Avatar
    Joined
    18 May 2013
    Posted:
    54 messages
    Followed by:
    1 members
    Post Tue Aug 06, 2013 8:25 am
    Matt@VeritasPrep wrote:
    One way of thinking about it:

    (10X + 8)/2 = (10X)/2 + 8/2 = 5x + 4

    Since you can break the sum into two fractions, you can break them up, then reduce each one individually.

    But (10X)/(8+2) is NOT (10x)/8 + (10x)/2, or (5/4)x + 5x ... it's (10X)/10, or x.

    So you CAN'T break these up into two fractions and reduce each part individually.

    As for fraction rules, how about:

    http://isites.harvard.edu/fs/docs/icb.topic760749.files/webAPPEodd.pdf
    It's clearly been a while since highschool algebra...

    Thanks.

    Best Conversation Starters

    1 abhasjha 41 topics
    2 shibsriz@gmail.com 31 topics
    3 phanikpk 18 topics
    4 qwerty12321 15 topics
    5 sapuna 14 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description GMATGuruNY

    The Princeton Review Teacher

    174 posts
    2 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    169 posts
    3 image description ceilidh.erickson

    Manhattan GMAT Teacher

    44 posts
    4 image description CriticalSquareMBA

    Critical Square

    36 posts
    5 image description lunarpower

    Manhattan GMAT Teacher

    30 posts
    See More Top Beat The GMAT Experts