Circular Gears (GPREP)

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zagcollins: Master | Next Rank: 500 Posts; Posts: 167; Joined: Wed Jun 11, 2008 10:58 pmFollowed by: 1 member; Thanked: 2 times

by zagcollins » Fri Aug 01, 2008 7:41 am

Circular gears P and R start rotating at the same time at constant speeds. Gear P makes 10 revolutions per minute while gear R makes 4 revolutions per minute. How many seconds after the gears start rotating will gear R have made exactly 6 more revolutions than gear P?
A.6
B.8
C.10
D.12
E.15

OA is 12..need explanation for the same...

Last edited by zagcollins on Fri Aug 01, 2008 7:21 pm, edited 1 time in total.

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Source: Beat The GMAT — Problem Solving | Fri Aug 01, 2008 7:41 am

sudhir3127: Legendary Member; Posts: 829; Joined: Mon Jul 07, 2008 10:09 pmFollowed by: 3 members; Location: INDIA; Thanked: 84 times

by sudhir3127 » Fri Aug 01, 2008 8:22 am

Are you sure abt the Question? i feel something is wrong in it ...

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raunekk: Legendary Member; Posts: 1159; Joined: Wed Apr 16, 2008 10:35 pm; Thanked: 56 times

by raunekk » Fri Aug 01, 2008 8:44 am

yup there is sumthg missing..

i thnk speed of R

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smclean23: Master | Next Rank: 500 Posts; Posts: 172; Joined: Mon Jun 23, 2008 12:00 pmFollowed by: 1 member; Thanked: 3 times

by smclean23 » Wed Oct 01, 2008 8:22 pm

Since gear P makes 1 revolution every 6 seconds and gear R makes 2 revolutions every 3 seconds, you can set up an equation like so:

Rate of Gear P *X (seconds) + 6 = Rate of Gear R * X(seconds)

1/6 X + 6 = 2/3 X

Solve for x=12

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vishubn: Legendary Member; Posts: 574; Joined: Sun Jun 01, 2008 8:48 am; Location: Bangalore; Thanked: 28 times

by vishubn » Wed Oct 01, 2008 9:35 pm

Since gear P makes 1 revolution every 6 seconds and gear R makes 2 revolutions every 3 seconds, you can set up an equation like so:

i agree with 1 rev every 6 seconds for p !!

but 2 rev every 3 sec

then according to this ! number of revolutions for R must be 40 not 4 ! if this a typo then i agree

if not somethings wrong with the question

Vishu

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vishubn: Legendary Member; Posts: 574; Joined: Sun Jun 01, 2008 8:48 am; Location: Bangalore; Thanked: 28 times

by vishubn » Wed Oct 01, 2008 9:42 pm

yes My assumption was right
there is typo in the question ! its not 4 revolution on R's part instead it is 40 !!!

and the solution also holds good

find the link

https://www.beatthegmat.com/rt-d-question-t19104.html

Hth

Vishu

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