BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

GMAT Prep?? (Circular Rotations)

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 446
Joined: Thu Jul 26, 2007 1:07 pm
Thanked: 6 times

GMAT Prep?? (Circular Rotations)

by dferm » Sun May 04, 2008 3:33 pm
Circular gears P and Q start rotating at the same time at constant speeds. Gear P makes 10 revolutions per minute, and gear Q makes 40 revolutions per minute. How many seconds after the gears start rotating will gear Q have made exactly 6 more revolutions than gear P?

A. 6
B. 8
C. 10
D. 12
E. 15

Please explain...

Got this question right but need a faster way...

Thanks.
Top
Source: — Problem Solving |
User avatar
Legendary Member
Posts: 519
Joined: Sat Jan 27, 2007 7:56 am
Location: India
Thanked: 31 times

by Neo2000 » Sun May 04, 2008 9:54 pm
P = 10/60 or 1R/6sec
Q = 40/60 or 2R/3sec = 4R/6sec

which means Q gains 3Revolutions every 6 seconds. For Q to gain 6, we need another 6seconds to pass. Which means 2sets of 6seconds have passed or 12seconds.
Ans : 12seconds
Top
Master | Next Rank: 500 Posts
Posts: 106
Joined: Sun Feb 17, 2008 10:09 pm
Thanked: 3 times

by ksh » Sun May 04, 2008 10:10 pm
For P 10/60 RPS = 1 Rev in 6 Sec

For Q 40/60 RPS = 4 rev in 6 Sec

In another 6 sec P will complete 2 Rev while Q will complete 8 Rev i.e. 6 more than P.

Hence, in 12 sec Q will be 6 Rev more than P.

Ans is D
Top
Post new topic Post Reply
• Page 1 of 1