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It takes 6 technicians a total of 10 hours to build and

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Re: It takes 6 technicians a total of 10 hours to build and  [#permalink]

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New post 15 Nov 2016, 20:09
Let's say job = 120 bricks --> Rate of 6 technicians then is --> 120=6R x 10 --> R = 2

5pm: 6(2)(6hrs) = 72
6pm: 6(2)(7hrs)+2 = 86
7pm: 6(2)(8)+2(2) +2 = 102
8pm: 6(2)(9)+2(3)+2(2)+2 =120 BINGO!

Answer is C
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Re: It takes 6 technicians a total of 10 hours to build and  [#permalink]

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New post 03 Feb 2017, 06:49
1) 6r*10=1s;,1s=60r
2) 6r*6=36r - 5pm
3) 36r+7r=43r - 6pm
5) 43r+8r=51r - 7pm
6) 51r+9r=60r - 8pm

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Re: It takes 6 technicians a total of 10 hours to build and  [#permalink]

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New post 08 Feb 2017, 19:44
Hussain15 wrote:
It takes 6 technicians a total of 10 hours to build and program a new server from Direct Computer, with each working at the same rate. If six technicians start to build the server at 11:00 AM, and one technician per hour is added beginning at 5:00 PM, at what time will the server be complete?

A. 7:30 PM
B. 7:45 PM
C. 8:00 PM
D. 9:00 AM
E. 10:00 PM


We are given that 6 technicians can complete a job in 10 hours. Since rate = work/time, the rate of the 6 technicians is 1/10. Thus, the rate of 1 technician is (1/10)/6 = 1/60.

We see that 6 technicians work from 11:00 AM to 5:00 PM, or 6 hours. Since rate x time = work, those technicians complete 1/10 x 6 = 6/10 = 3/5 of the job.

If another technician is added to the job at 5:00 PM, the new rate for the technicians is (1/60) x 7 = 7/60, and thus all 7 technicians complete 7/60 of the job in the hour from 5:00 PM to 6:00 PM.

Thus, 3/5 + 7/60 = 36/60 + 7/60 = 43/60 of the job will be completed.

If another technician is added to the job at 6:00 PM, the new rate for the technicians is (1/60) x 8 = 8/60, and thus all 8 technicians complete 8/60 of the job in the hour from 6:00 PM to 7:00 PM.

Thus, 43/60 + 8/60 = 51/60 of the job will be completed.

If another technician is added to the job at 7:00 PM, the new rate for the technicians is (1/60) x 9 = 9/60, and thus all 9 technicians complete 9/60 of the job in the hour from 7:00 PM to 8:00 PM.

Thus, 51/60 + 9/60 = 60/60 = 1 whole job will be completed at 8:00 PM.

Answer: C
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Re: It takes 6 technicians a total of 10 hours to build and  [#permalink]

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New post 06 Jun 2017, 16:54
Hussain15 wrote:
It takes 6 technicians a total of 10 hours to build and program a new server from Direct Computer, with each working at the same rate. If six technicians start to build the server at 11:00 AM, and one technician per hour is added beginning at 5:00 PM, at what time will the server be complete?

A. 7:30 PM
B. 7:45 PM
C. 8:00 PM
D. 9:00 AM
E. 10:00 PM

1. 1 technician will build in 60 hours or 60 man hours are needed
2. 6 technicians work for first 6 hours which is expending of 36 man hours
3. Similarly in the seventh, eighth , ninth hours, man hours expended are 7,8,9
4. Total man hours expended by the end of ninth hour is 36+7+8+9= 60 which will complete the job.
5. 11 A.M + 9 hrs is 8 PM
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Re: It takes 6 technicians a total of 10 hours to build and  [#permalink]

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New post 09 Aug 2019, 17:46
Bunuel wrote:
Hussain15 wrote:
It takes 6 technicians a total of 10 hours to build and program a new server from Direct Computer, with each working at the same rate. If six technicians start to build the server at 11:00 AM, and one technician per hour is added beginning at 5:00 PM, at what time will the server be complete?

A. 7:30 PM
B. 7:45 PM
C. 8:00 PM
D. 9:00 AM
E. 10:00 PM


To complete the job 6*10=60 man/hours are needed. By 5:00 PM 6*6=36 man/hour done. 24 is left.

5:00 PM - 6:00 PM 7 man/hour;
6:00 PM - 7:00 PM 8 man/hour;
7:00 PM - 8:00 PM 9 man/hour.

7+8+9=24.

Answer: C.


How can you recognize when to solve this kind of problem in that way and no with the work/rate approach (below)?

I started computing the rate for 6, 7, 8, 9 and 10 man:

r6 = 1/10
r7 = 1/10 + 1/60 = 7/60
r8 = 8/60
r9 = 9/60
r10 = 1/6

There, I already invested 1.5 minutes trying to solve the problem. And I still need to calculate the work done for 6pm, 7pm, 8pm, 9pm, and then sum all of it and see the at what time the server is complete..

Can you give me some insight?

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Re: It takes 6 technicians a total of 10 hours to build and  [#permalink]

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New post 10 Aug 2019, 10:01
1
RT = W
6r10 = W
r =W /60

Technically Speaking, you require 60 man hours for the job which is the essence of the last equation.
Now From 11 AM to 5 PM . 6*6 = 36 manhours are already given.
So Remaining 60 - 36 = 24 hrs have to be done.

5-6 => 7 man hours
6-7 => 8 man hrs
7-8 => 9 man hrs

SO total = 7+8+9 = 24 hrs
Hence Answer = 8 PM.
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Re: It takes 6 technicians a total of 10 hours to build and   [#permalink] 10 Aug 2019, 10:01

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