least distance problem-GMAT PREP

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rashmi.kaushal: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Tue May 06, 2008 1:57 am; Thanked: 4 times

least distance problem-GMAT PREP

by rashmi.kaushal » Wed Aug 11, 2010 3:10 am

Can somebody explain pl ?

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Source: Beat The GMAT — Problem Solving | Wed Aug 11, 2010 3:10 am

clock60: Legendary Member; Posts: 759; Joined: Mon Apr 26, 2010 10:15 am; Thanked: 85 times; Followed by:3 members

by clock60 » Wed Aug 11, 2010 3:26 am

one possible way to solve is to find LCM of 7 and 5, it must be 35
and then list all multiples of 5 and 7 between 1 and 35
for 5 it must be 5. 10. 15. 20. 25.30.35
for 7 1, 14, 21, 28, 35
the least distance 21-20=1. or 15-14=1
so desired answer 1/35

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rashmi.kaushal: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Tue May 06, 2008 1:57 am; Thanked: 4 times

by rashmi.kaushal » Wed Aug 11, 2010 4:00 am

clock60 wrote:one possible way to solve is to find LCM of 7 and 5, it must be 35
and then list all multiples of 5 and 7 between 1 and 35
for 5 it must be 5. 10. 15. 20. 25.30.35
for 7 1, 14, 21, 28, 35
the least distance 21-20=1. or 15-14=1
so desired answer 1/35

Thanks, for maximum distance (35-1)/35 ?? correct ?

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selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 am; Thanked: 135 times; Followed by:7 members

by selango » Wed Aug 11, 2010 4:08 am

Large tick marks are divided into fifths:1/5,2/5,3/5,4/5,5/5

Small tick marks are divided into sevenths:1/7,2/7,3/7,4/7,5/7,6/7,7/7

LCM(5,7)=35 and have a common denominator on both terms.

-->Large tick marks:7/35,14/35,21/35,28/35,35/35

-->Small tick marks:5/35,10/35,15/35,20/35,25/35,30/35,35/35

Least distance =21/35-20/35=1/35

--Anand--