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# It takes Computer A 36 hours to process data. If Computer A starts wor

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It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  07 Aug 2008, 21:31
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It takes Computer A 36 hours to process data. If Computer A starts working at 7 pm on Monday and after half the data are processed Computer B, three times as fast as Computer A, joins in the task, when will the data processing be finished?

A. 4:30 pm Tuesday
B. 5:30 pm Tuesday
C. 7:00 pm Tuesday
D. 8:30 pm Tuesday
E. 10:30 pm Tuesday

M18-12
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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  07 Aug 2008, 21:40
mba9now wrote:
It would take Computer A 36 hours to process the data. If Computer A starts working at 7 pm on Monday and after half the data is processed Computer B, three times as fast as Computer A, is joined in the task, when will the data processing be finished?

4:30 pm Tuesday
5:30 pm Tuesday
7:00 pm Tuesday
8:30 pm Tuesday
10:30 pm Tuesday

comp A takes 36h and comp B takes 12h

comp A starts at 7pm on monday, processes half the data so it finishes at 7pm+(36/2)h which is 1pm on tuesday. Comp B takes up the next half so it finishes at 1pm+(12/2)h=7pm on Tuesday
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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  07 Aug 2008, 21:54
The answer is B (5:30 PM Tuesday). Becasue it is said that Comp B joins A, never says only B did the work alone.
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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  08 Aug 2008, 07:42
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mba9now wrote:
It would take Computer A 36 hours to process the data. If Computer A starts working at 7 pm on Monday and after half the data is processed Computer B, three times as fast as Computer A, is joined in the task, when will the data processing be finished?

4:30 pm Tuesday
5:30 pm Tuesday
7:00 pm Tuesday
8:30 pm Tuesday
10:30 pm Tuesday

computer A take 36 hr
computer B takes 12 hr

18 hrs (half job done by computer) + Half job dont by both
= 18 hrs + 18 / (3+1) = 22.5 hrs.

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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  08 Aug 2008, 20:17
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mba9now wrote:
It would take Computer A 36 hours to process the data. If Computer A starts working at 7 pm on Monday and after half the data is processed Computer B, three times as fast as Computer A, is joined in the task, when will the data processing be finished?

4:30 pm Tuesday
5:30 pm Tuesday
7:00 pm Tuesday
8:30 pm Tuesday
10:30 pm Tuesday

work done by A in one hr = w/36
by B in 1 hr=w/12
by both in 1 hr=w/12 + w/36=w/9

hence half the work is already done by A in 18 hrs

half the work w/2 is to be done by both hence time talken is w/2/w/9=9/2=4.5 hrs
total time taken is 18+4.5 hrs=22.5 hrs
IMO B
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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  08 Aug 2008, 22:07
mba9now wrote:
It would take Computer A 36 hours to process the data. If Computer A starts working at 7 pm on Monday and after half the data is processed Computer B, three times as fast as Computer A, is joined in the task, when will the data processing be finished?

4:30 pm Tuesday
5:30 pm Tuesday
7:00 pm Tuesday
8:30 pm Tuesday
10:30 pm Tuesday

Total hrs = 18 + Hours required to do half job = 18 + (18*6)/24 = 22.5 hrs = 5:30pm Tue
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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  09 Nov 2014, 11:29
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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  10 Nov 2014, 01:38
Expert's post
It takes Computer A 36 hours to process data. If Computer A starts working at 7 pm on Monday and after half the data are processed Computer B, three times as fast as Computer A, joins in the task, when will the data processing be finished?

A. 4:30 pm Tuesday
B. 5:30 pm Tuesday
C. 7:00 pm Tuesday
D. 8:30 pm Tuesday
E. 10:30 pm Tuesday

Computer A will process the first half of the data in 18 hours. Computer A and Computer B working together will process the remaining half four times quicker than will Computer A working alone. The entire task will require $$18 + \frac{18}{4} = 22.5$$ hours which is 1.5 hours short of the 24-hour cycle. If the processing commences at 7 pm on Monday, it will finish at 5:30 pm on Tuesday.

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Re: It takes Computer A 36 hours to process data. If Computer A starts wor [#permalink]  12 Nov 2014, 01:25
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Rate of Computer A = $$\frac{1}{36}$$

Rate of Computer B = $$\frac{1}{12}$$

$$\frac{1}{2}$$ Job completed by Computer A alone; means time consumed by Computer A $$= \frac{1}{2} * 36 = 18$$ Hrs

Combined rate of A & B $$= (\frac{1}{36} + \frac{1}{12}) = \frac{1}{9}$$

Time required to complete remaining $$\frac{1}{2}$$ Job $$= \frac{1}{2} * \frac{9}{1} = 4.5 Hrs$$

Total Time required to complete job = 18 + 4.5 = 22.5 Hrs

24 Hrs is SAME TIME next day, so 22.5 Hrs would be

7PM Tuesday - 1.5 Hrs = 5:30 PM Tuesday

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Re: It takes Computer A 36 hours to process data. If Computer A starts wor   [#permalink] 12 Nov 2014, 01:25
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