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Circular Gears P and Q start rotating at the same time at

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Re: How many seconds after the gears start rotating?  [#permalink]

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New post 02 Jan 2011, 03:33
2

Q does 30 more rev per min than P does ... so it does 1/2 rev more each sec
for 6 rev more ... Q will thus need 6/0.5 = 12secs

30 more .... 60 secs
1/2 more ... 1 sec
6 more ... 12 secs

you can do this in under 40secs
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Re: How many seconds after the gears start rotating?  [#permalink]

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New post 05 Jan 2011, 01:40
Gear P

60sec--10rev
1sec=1/6 rev

Gear Q
60 sec--40 rev
1sec=2/3 rev

Gear q-Gear p=6
x(1/6)-x(2/3)=6----'x' is sec

X=12---Ans D
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Re: How many seconds after the gears start rotating?  [#permalink]

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New post 05 Jan 2011, 03:09
Gear P .... in 60 seconds 10 rev.... 1 sec 1/6 rev
gear Q .... in 60 seconds 40 rev.... 1 sec 40/60 =2/3 rev

Difference of rev in one sec = 2/3 - 1/6 = 1/2 rev

1/2 revolution more for Gear Q than P in 1 sec
1 revolution more for Gear Q than P in 2 sec
6 revolutions more for Gear Q than P = 2 * 6 = 12 seconds.

So Answer is (D)
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Re: Gmat prep circular gears  [#permalink]

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New post 05 Aug 2011, 11:23
p - 10 rev/min

q - 40 rev/min

in x min , p would make 10x revolutions

q would make 40x revolutions


given 40x = 10x+6

=> x = 1/5 mins
=12 seconds

Answer is D.
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Re: Revolutions per minute problem  [#permalink]

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New post 05 Aug 2011, 12:26
gear p makes 1/6 rev per sec
gear q makes 2/3 rev per sec

assume t is time elapsed in seconds..

6 = 2t/3 - t/6 => t = 12 sec..
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Re: Gmat prep circular gears  [#permalink]

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New post 05 Aug 2011, 13:27
Equation can be set up as follows
(40/60-10/60)x=6.
(30/60)x=6
1/2 x=6
x=12
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GMAT Prep PS: Circular Gears P and Q revolutions  [#permalink]

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New post 10 Oct 2011, 03:18
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) 9
(B) 10
(C) 12
(D) 14
(E) 15
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Re: Revolutions  [#permalink]

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New post 10 Oct 2011, 05:28
I'll take shot. Answer is C:

Here is why:

Gear P makes 1 revolution for every 6 secs
Gear q makes 1 revolutions for every 1.5 secs; that means for every 6 secs it makes it makes 4 revolution

so p make 1 revolution for 6 secs and q 4 revs. diffrence 3. But we are asked for difference of 6 revs.

so doubling the above equation:
12secs - 2 revs -- P
12 secs - 8 revs - Q difference is 6.

Ans c.

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Re: Revolutions  [#permalink]

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New post 10 Oct 2011, 05:33
jiv wrote:
1) 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?
a) 9
b) 10
c) 12
d) 14
e) 15

Can anyone help me get this resolved?

Thanks


In one minute - Q makes 30 more revolutions than P (40-10).

.i.e. so if Q needs to make 6 revolutions more than P - 60 sec/5 = 12 sec.

Let me know if you have any questions
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Re: Circular Gears P and Q start rotating at the same time at  [#permalink]

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New post 21 Dec 2011, 09:17
30 revelation in 60 seconds
so, 6 revelation in =[60/30]*6 = 12
Ans. D
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Re: Circular Gears P and Q start rotating at the same time at  [#permalink]

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New post 21 Dec 2011, 10:17
after 60 sec Q makes 30 rev. more than p.
i. e. for q to make 6 rev. more, it will take (60*6)/30=12 sec.
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Re: Circular Gears P and Q start rotating at the same time at  [#permalink]

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New post 11 Aug 2018, 13:42
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Re: Circular Gears P and Q start rotating at the same time at &nbs [#permalink] 11 Aug 2018, 13:42

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