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Machines A, B, and C can either load nails into a bin or unload nails [#permalink]
30 Nov 2009, 06:57

00:00

A

B

C

D

E

Difficulty:

(N/A)

Question Stats:

83% (03:31) correct
17% (02:11) wrong based on 30 sessions

Machines A, B, and C can either load nails into a bin or unload nails from that bin. Each machine works at a constant rate that is the same for loading and for unloading, although the individual machines may have different rates. Working together to load at their respective constant rates, machines A and B can load the bin in 6 minutes. Likewise, working together to load at their respective constant rates, machines B and C can load the bin in 9 minutes. How long will it take machine A to load the bin if machine C is simultaneously unloading the bin?

Re: Machines A, B, and C can either load nails into a bin or unload nails [#permalink]
30 Nov 2009, 07:18

1

This post received KUDOS

kirankp wrote:

I guess a similar question was posted by Bunel sometime back.. anyhow here it is

Machines A, B, and C can either load nails into a bin or unload nails from that bin. Each machine works at a constant rate that is the same for loading and for unloading, although the individual machines may have different rates. Working together to load at their respective constant rates, machines A and B can load the bin in 6 minutes. Likewise, working together to load at their respective constant rates, machines B and C can load the bin in 9 minutes. How long will it take machine A to load the bin if machine C is simultaneously unloading the bin? (A) 12 minutes (B) 15 minutes (C) 18 minutes (D) 36 minutes (E) 54 minutes

answer C

A and B together = 1/a + 1/b = 1/6

B and C together = 1/b + 1/c = 1/9

We need to know the answer to 1/a - 1/c

From equation 2: 1/b = 1/9 - 1/c substitute into equation 1

Re: Machines A, B, and C can either load nails into a bin or unload nails [#permalink]
25 Jun 2015, 07:42

1

This post received KUDOS

kirankp wrote:

I guess a similar question was posted by Bunuel sometime back.. anyhow here it is

Machines A, B, and C can either load nails into a bin or unload nails from that bin. Each machine works at a constant rate that is the same for loading and for unloading, although the individual machines may have different rates. Working together to load at their respective constant rates, machines A and B can load the bin in 6 minutes. Likewise, working together to load at their respective constant rates, machines B and C can load the bin in 9 minutes. How long will it take machine A to load the bin if machine C is simultaneously unloading the bin? (A) 12 minutes (B) 15 minutes (C) 18 minutes (D) 36 minutes (E) 54 minutes

Bumping up. Moderator should edit in answer. \(\frac{1}{6}\) - \(\frac{1}{9}\) = \(\frac{1}{18}\) D. 18 minutes.

This works because \(\frac{a+b}{ab}\) - \(\frac{b+c}{bc}\) = \(\frac{c-a}{ac}\) and \(\frac{1}{a}\) - \(\frac{1}{c}\) = \(\frac{c-a}{ac}\) _________________

+1 Kudos if my comment was helpful. Thanks!

Failure forges confidence, and confidence cultivates success. Proving the answer choices wrong is almost better than calculating what is right.

Re: Machines A, B, and C can either load nails into a bin or unload nails [#permalink]
25 Jun 2015, 07:49

mejia401 wrote:

kirankp wrote:

I guess a similar question was posted by Bunuel sometime back.. anyhow here it is

Machines A, B, and C can either load nails into a bin or unload nails from that bin. Each machine works at a constant rate that is the same for loading and for unloading, although the individual machines may have different rates. Working together to load at their respective constant rates, machines A and B can load the bin in 6 minutes. Likewise, working together to load at their respective constant rates, machines B and C can load the bin in 9 minutes. How long will it take machine A to load the bin if machine C is simultaneously unloading the bin? (A) 12 minutes (B) 15 minutes (C) 18 minutes (D) 36 minutes (E) 54 minutes

Bumping up. Moderator should edit in answer. \(\frac{1}{6}\) - \(\frac{1}{9}\) = \(\frac{1}{18}\) D. 18 minutes.

This works because \(\frac{a+b}{ab}\) - \(\frac{b+c}{bc}\) = \(\frac{c-a}{ac}\) and \(\frac{1}{a}\) - \(\frac{1}{c}\) = \(\frac{c-a}{ac}\)

Ans is ok as it is it is C which is 18 and D is 36...

gmatclubot

Re: Machines A, B, and C can either load nails into a bin or unload nails
[#permalink]
25 Jun 2015, 07:49

Originally posted on MIT Sloan School of Management : We are busy putting the final touches on our application. We plan to have it go live by July 15...