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gibran · 07-11-2008, 07:06 PM

Three machines have the identical rate. If two of them work together, it takes k hours to complete a certain work. If all of them work together, it takes two hours less to complete the same work. K=?
(A) 4
(B) 6
(C) 10
(D) 12
(E) 14

OA:

SPOILER: B

suwarnapatel · 07-11-2008, 07:17 PM

Take time for each machine to complete Job = X
Therefore Rate of each machine = 1/X

When 2 Machines Work Together:

1/X + 1/X = 1/K
2/X=1/K
X=2K

Similarly
When 3 Machines Work Together:

3/X = 1/(K-2)
3/2K=1/(K-2)

3K-6=2K
K=6

ddyno · 07-12-2008, 09:08 AM

Same approach. Same ans

bose · 07-12-2008, 07:27 PM

solved it like suwarna got ans B

GmatG · 07-14-2008, 06:41 AM

IMO B Same as above

nikhilsikri · 07-20-2008, 08:09 PM

1/3 k = 2 so k =6 ....

Retake_GMAT · 07-21-2008, 03:04 AM

Since rate of all machines are same, time is also same. let x be the time taken to do the job.

1/k = 1/x + 1/x = 2/x.........eq 1

1/(k -2) = 3/x...................eq2

In eq2 put x=2k.

we get k=6

CallMeDaOne · 07-21-2008, 06:36 AM

IMO B is the answer.

Anson800 · 07-24-2008, 07:21 AM

Say m is rate; then 2/m=1/k and 3/m=1/k-2; after solving ans=6 i.e. B

07-11-2008, 07:06 PM	#1 (permalink)
gibran Within my grasp! Join Date: Nov 2005 Posts: 280	rate problem Three machines have the identical rate. If two of them work together, it takes k hours to complete a certain work. If all of them work together, it takes two hours less to complete the same work. K=? (A) 4 (B) 6 (C) 10 (D) 12 (E) 14 OA: SPOILER: B

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07-11-2008, 07:17 PM	#2 (permalink)
suwarnapatel Eager! Join Date: Jul 2008 Posts: 96	Take time for each machine to complete Job = X Therefore Rate of each machine = 1/X When 2 Machines Work Together: 1/X + 1/X = 1/K 2/X=1/K X=2K Similarly When 3 Machines Work Together: 3/X = 1/(K-2) 3/2K=1/(K-2) 3K-6=2K K=6

07-12-2008, 09:08 AM	#3 (permalink)
ddyno Eager! Join Date: Jun 2008 Posts: 60	Same approach. Same ans

07-12-2008, 07:27 PM	#4 (permalink)
bose TestMagic Guru-in-Training Join Date: Dec 2006 Posts: 614	solved it like suwarna got ans B

07-14-2008, 06:41 AM	#5 (permalink)
GmatG Within my grasp! Join Date: Oct 2007 Posts: 122	IMO B Same as above

07-20-2008, 08:09 PM	#6 (permalink)
nikhilsikri Trying to make mom and pop proud Join Date: Jul 2008 Posts: 29	1/3 k = 2 so k =6 ....

07-21-2008, 03:04 AM	#7 (permalink)
Retake_GMAT Struggling Hard Join Date: May 2008 Location: India, Bangalore Posts: 465	Since rate of all machines are same, time is also same. let x be the time taken to do the job. 1/k = 1/x + 1/x = 2/x.........eq 1 1/(k -2) = 3/x...................eq2 In eq2 put x=2k. we get k=6

07-21-2008, 06:36 AM	#8 (permalink)
CallMeDaOne Set The Wheels Rolling! Join Date: Jul 2008 Location: Buzzing Mumbai. Posts: 39	IMO B is the answer.

07-24-2008, 07:21 AM	#9 (permalink)
Anson800 WIll do it Join Date: May 2008 Location: Singapore Posts: 125	Say m is rate; then 2/m=1/k and 3/m=1/k-2; after solving ans=6 i.e. B

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