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Tom, working alone, can paint a room in 6 hours. Peter and John [#permalink]

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27 Jan 2012, 12:19

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Tom, working alone, can paint a room in 6 hours. Peter and John, working independently, can paint the same room in 3 hours and 2 hours, respectively. Tom starts painting the room and works on his own for one hour. He is then joined by Peter and they work together for an hour. Finally, John joins them and the three of them work together to finish the room, each one working at his respective rate. What fraction of the whole job was done by Peter?

First Hr : T starts working and in 1 hour can finish 1/6 of the job

Second Hr: T & P starts working and in an hr can finish 1/6+1/3 = 3/6 of the job. So Total 4/6 of the job is finished by now

Third Hr: T,P & J starts working but they have only 2/6 of the job remaining. Working together they need one hr to finish the entire job (work formula 1/6+1/3+1/2 = 1/1 = 1 hr) so they work only for 2/6 of an hour. THerefore peter working at a rate of 1/3 can do only 1/3*2/6 = 1/9 of the job before the job is finished.

Tom, working alone, can paint a room in 6 hours. Peter and John, working independently, can paint the same room in 3 hours and 2 hours, respectively. Tom starts painting the room and works on his own for one hour. He is then joined by Peter and they work together for an hour. Finally, John joins them and the three of them work together to finish the room, each one working at his respective rate. What fraction of the whole job was done by Peter?

A. 1/9 B. 1/6 C. 1/3 D. 7/18 E. 4/9

Let the time when all three were working together be t hours. Then:

Tom worked for t+2 hours and has done 1/6*(t+2) part of the job; Peter worked for t+1 hours and has done 1/3*(t+1) part of the job; John worked for t hours and has done 1/2*t part of the job:

\(\frac{1}{6}*(t+2)+\frac{1}{3}*(t+1)+\frac{1}{2}*t=1\) Multiply by 6: \((t+2)+(2t+2)+3t=6\); \(t=\frac{1}{3}\).

Hence Peter has done \(\frac{1}{3}*(\frac{1}{3}+1)=\frac{4}{9}\) part of the job.

time left with all three: \(\frac{1}{6}+\frac{1}{3}+\frac{1}{2}(t)=1/3==>t=\frac{1}{3}hr\)

Therefore, Peter worked for \(1\frac{1}{3}hr==>W=\frac{1}{3}(1\frac{1}{3})=\frac{4}{9}\)

Answer:E

Could you please explain after the 1/3 remaining. I understood until all 3 complete 1 work together,so from this point on wards what is the work remaining ?

Previous case tom and peter complete (1/6+1/3) in one hour so total work completed is (1/6+1/2) is 2/3 , now when peter,tom and jack together work (1/6+1/2+1/3) is 1.Does that mean work gets completed when peter comes in,should the work be added 2/3+1 .

1/3 work is to be completed so how do you proceed from here. Thanks.

Tom, working alone, can paint a room in 6 hours. :- Tom is finishing 100/6 i.e. 16.66% of the work in 1 hour.

Peter, working independently, can paint the same room in 3 hours. :- Peter is finishing 100/3 i.e. 33.33% of the work in 1 hour.

John, working independently, can paint the same room in 2 hours. :- Tom is finishing 100/2 i.e. 50% of the work in 1 hour.

Tom starts painting the room and works on his own for one hour. :- Tom Completed 16.66 of the work. 83.34% work is balance

He is then joined by Peter and they work together for an hour. :- Tom + Peter Completed (16.66% + 33.33% = 50%) of the work. 33.33% work is balance Finally, John joins them and the three of them work together to finish the room :- Together Tom + Peter + John Complete (16.66% + 33.33% + 50= 100%) work in 1 hour, So to finish balance 33.33% work it would take them \(\frac{33.33}{100} = \frac{1}{3} hour.\)

What fraction of the whole job was done by Peter? :- We know Peter worked for \(1 + \frac{1}{3} hour.\) He must have completed \(33.33 + \frac{1}{3}(33.33)\) work ------> He completed 44.44% work which equals to \(\frac{4}{9}\)
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Re: Tom, working alone, can paint a room in 6 hours. Peter and John [#permalink]

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29 Nov 2015, 12:14

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Let's use smart numbers here --> Work=18 Rate * Time = Work Tom: 3 x 6 = 18 Peter: 6 x 3 = 18 John: 9 x 2 = 18

Before John joined Tom and Peter: Tom worked 2 Hours -> 2*3=6 and Peter 1*6=6 gives us 12. So we are left with 18-12=6 for all three of them --> (3+6+9)*t=6, thus t=1/3 this means that Peter worked 2+1/3 Hours = 6+2=8 --> 8/18=4/9 At least this approach helps me... Don't like dealind with fractions when you're tired.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and John [#permalink]

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07 Apr 2017, 12:54

Let`s first put some value to the area of the room to make this problem easier to solve. We are looking for a value that is advisable by the working rate of each one, Tom =6, Peter = 3, and John = 2. So the best value for the room area is 6x3x2 = 36 feet. Tom starts painting the room and works on his own for one hour, so he paint 6 feet of the room, and 30 feet is the remaining. He is then joined by Peter and they work together for an hour, so Tom paint another 6 feet, Peter paint 12 feet, and 30 – 6 -12 = 12 feet is the remaining. Finally, John joins them and the three of them work together to finish the room, each one working at his respective rate. Here we need to divide the remaining 6 feet among Tom, Peter and John based on their working rate. Tom = 12/6 = 2 feet, Peter = 12/3 = 4 feet, and John = 12/2 =6feet. What fraction of the whole job was done by Peter? Peter fraction = (12+4)/36 =4/9 ---D

Last edited by nawaf52 on 08 Apr 2017, 19:20, edited 1 time in total.

Re: Tom, working alone, can paint a room in 6 hours. Peter and John [#permalink]

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07 Apr 2017, 13:03

So i used different approach. I wasnt able to solve it, but brought it down to two options. If peter worked for one hour thats 33% of work and he worked with tom n john after that so technically he finished more than 33%. That eliminates A,B and C.

And then i guessed D. I know its a wrong answer but better chance at guessing out of 2 than out of 5.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and John [#permalink]

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27 May 2017, 17:50

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Tom's individual rate is 1 job / 6 hours or 1/6. During the hour that Tom works alone, he completes 1/6 of the job (using rt = w).

Peter's individual rate is 1 job / 3 hours. Peter joins Tom and they work together for another hour; Peter and Tom's respective individual rates can be added together to calculate their combined rate: 1/6 + 1/3 = 1/2. Working together then they will complete 1/2 of the job in the 1 hour they work together.

At this point, 2/3 of the job has been completed (1/6 by Peter alone + 1/2 by Peter and Tom), and 1/3 remains.

When John joins Tom and Peter, the new combined rate for all three is: 1/6 + 1/3 + 1/2 = 1. The time that it will take them to finish the remaining 1/3 of the job can be solved: rt = w (1)(t) = 1/3 t = 1/3.

The question asks us for the fraction of the job that Peter completed. In the hour that Peter worked with Tom he alone completed: rt = w w = (1/3)(1) = 1/3 of the job. In the last 1/3 of an hour that all three worked together, Peter alone completed: (1/3)(1/3) = 1/9 of the job. Adding these two values together, we get 1/3 + 1/9 of the job = 4/9 of the job.

The correct answer is E.
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Tom, working alone, can paint a room in 6 hours. Peter and John, working independently, can paint the same room in 3 hours and 2 hours, respectively. Tom starts painting the room and works on his own for one hour. He is then joined by Peter and they work together for an hour. Finally, John joins them and the three of them work together to finish the room, each one working at his respective rate. What fraction of the whole job was done by Peter?

A. 1/9 B. 1/6 C. 1/3 D. 7/18 E. 4/9

Let the time when all three were working together be t hours. Then:

Tom worked for t+2 hours and has done 1/6*(t+2) part of the job; Peter worked for t+1 hours and has done 1/3*(t+1) part of the job; John worked for t hours and has done 1/2*t part of the job:

\(\frac{1}{6}*(t+2)+\frac{1}{3}*(t+1)+\frac{1}{2}*t=1\) Multiply by 6: \((t+2)+(2t+2)+3t=6\); \(t=\frac{1}{3}\).

Hence Peter has done \(\frac{1}{3}*(\frac{1}{3}+1)=\frac{4}{9}\) part of the job.

Answer: E.

Hence Peter has done 1/3*(1/3+1)=4/9 part of the job.

can you explain this part please?

Peter worked for t+1 hours at the rate of 1/3 job hour, so in t+1 hour and has done 1/3*(t+1) part of the job. t = 1/3, so he's done \(time*rate=\frac{1}{3}*(\frac{1}{3}+1)=\frac{4}{9}\) part of the job.