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While working alone at their constant rates computer X can process 240

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While working alone at their constant rates computer X can process 240 [#permalink]

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New post 29 Mar 2011, 04:36
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Question Stats:

86% (00:54) correct 14% (01:34) wrong based on 316 sessions

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While working alone at their constant rates computer X can process 240 files in 4 hours, and comp Y 240 files in 8 hrs. If all files processed by these comp. are the same size how long would it take the two comp. working at the same time at their respective constant rates , to process a total of 240 files?

A. 2hrs
B. 2hrs 20 min
C. 2hrs 40 min
D. 6hrs
E. 6hrs 20 min

[Reveal] Spoiler:
i did as under
X in one hour = 240/4 = 60 files
Y in one hour = 240/8 = 30 fles
X+ Y in one hour 60+30=90 files
So together they will take (240/90)= 2 hours 40 minutes.
So C is the answer.
I do not know the OA.
Am I right?
[Reveal] Spoiler: OA

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Last edited by Bunuel on 16 Dec 2014, 03:53, edited 1 time in total.
Renamed the topic, edited the question and added the OA.

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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 29 Mar 2011, 04:49
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Yes, your answer is correct.

Btw, 240 files information is irrelevant here, as both do the same work, it can be regarded as 1 unit of work.

In 1 hr, both finish = 1/8 + 1/4 = (1+2)/8 part of work

So total in 8/3 hrs

= 2 2/3 hrs

= 2 hrs 40 min
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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 29 Mar 2011, 05:14
Baten80 wrote:
While working alone at their constant rates computer X can process 240 files in 4 hours, and comp Y 240 files in 8 hrs. If all files processed by these comp. are the same size how long would it take the two comp. working at the same time at their respective constant rates , to process a total of 240 files?

2hrs
2hrs 20 min
2hrs 40 min
6hrs
6hrs 20 min

i did as under
X in one hour = 240/4 = 60 files
Y in one hour = 240/8 = 30 fles
X+ Y in one hour 60+30=90 files
So together they will take (240/90)= 2 hours 40 minutes.
So C is the answer.
I do not know the OA.
Am I right?


Computer 1 processes 60 files an hour
Computer 2 processes 30 files an hour

Combined they will process 90 files an hour

For 240 files, they will take (240/9) hours ... which is 2h40m
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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 29 Mar 2011, 05:47
Baten80 wrote:
While working alone at their constant rates computer X can process 240 files in 4 hours, and comp Y 240 files in 8 hrs. If all files processed by these comp. are the same size how long would it take the two comp. working at the same time at their respective constant rates , to process a total of 240 files?

2hrs
2hrs 20 min
2hrs 40 min
6hrs
6hrs 20 min

i did as under
X in one hour = 240/4 = 60 files
Y in one hour = 240/8 = 30 fles
X+ Y in one hour 60+30=90 files
So together they will take (240/90)= 2 hours 40 minutes.
So C is the answer.
I do not know the OA.
Am I right?


Yes, you are right.

You have solved it by unitary method;

90 files -> 1 hour
1 file -> 1/90 hour
240 files -> (1/90)* 240 hours
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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 06 Apr 2011, 07:25
X - 60 files per hour
Y - 30 files per hour
X & Y together - 90 files per hour
90+90=180
We need 60 more
So 60/90 of an hour i.e. 2/3 of an hour = 40 min
So 2 hours and 40 min...

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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 11 Aug 2011, 06:42
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X does 240 in 4hrs = 60 in 1 hr
Y does 240 in 8hrs = 30 in 1hr

X+Y = 90 in 1hr
240 in = 240/90 = 2.6666 hrs = 2hrs 40mins
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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 11 Aug 2011, 16:03
subhashghosh wrote:
Yes, your answer is correct.

Btw, 240 files information is irrelevant here, as both do the same work, it can be regarded as 1 unit of work.

In 1 hr, both finish = 1/8 + 1/4 = (1+2)/8 part of work

So total in 8/3 hrs

= 2 2/3 hrs

= 2 hrs 40 min


I like this approach. But can someone tell me why 3/8 was flipped to 8/3 to get the final answer?

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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 11 Aug 2011, 16:11
X 60 files/hour
Y 30 files/hour

together , they will take 240/(60+30) hours to process 240 files

= 240/90 = 2hr 40 min

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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 11 Aug 2011, 16:25
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Here we are considering work as 1 unit of work.

X --- does 1 unit of work in 4 hours => rate of x = 1/4
Y ---- does 1 unit of work in 8 hours =>rate of y = 1/8


together
their rate is 1/4+1/8 = 3/8
work - same 1 unit of work = 1
time it will take do the unit work = 1/(3/8) = 8/3 hours

Hope its clear now.



aks1985 wrote:
subhashghosh wrote:
Yes, your answer is correct.

Btw, 240 files information is irrelevant here, as both do the same work, it can be regarded as 1 unit of work.

In 1 hr, both finish = 1/8 + 1/4 = (1+2)/8 part of work

So total in 8/3 hrs

= 2 2/3 hrs

= 2 hrs 40 min


I like this approach. But can someone tell me why 3/8 was flipped to 8/3 to get the final answer?

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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 11 Aug 2011, 23:45
X in 1 hr = 60 and y in 1 hr = 30 files.
in 2 hrs X + Y = 120 + 60 = 180
remaining = 60

hence in 40 mins X + Y = 40 + 20 = 60

thus 2:40 C is the cue.
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Re: While working alone at their constant rates computer X can process 240 [#permalink]

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New post 05 Nov 2017, 08:21
Baten80 wrote:
While working alone at their constant rates computer X can process 240 files in 4 hours, and comp Y 240 files in 8 hrs. If all files processed by these comp. are the same size how long would it take the two comp. working at the same time at their respective constant rates , to process a total of 240 files?

A. 2hrs
B. 2hrs 20 min
C. 2hrs 40 min
D. 6hrs
E. 6hrs 20 min


The rate of computer X is 240/4 = 60 files in 1 hour and the rate of computer Y is 240/8 = 30 files in 1 hour, so the combined rate is 90 files in 1 hour. Thus, it takes 240/90 = 2 60/90 hours = 2 ⅔ hours = 2 hours and 40 minutes to complete 240 files when both computers work together.

Answer: C
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Re: While working alone at their constant rates computer X can process 240   [#permalink] 05 Nov 2017, 08:21
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