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Tom, working alone, can paint a room in 6 hours. Peter and

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Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 11 Aug 2011, 07:40
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Question Stats:

53% (07:40) correct 47% (02:54) wrong based on 68 sessions
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

OPEN DISCUSSION OF THIS QUESTION IS HERE: tom-working-alone-can-paint-a-room-in-6-hours-peter-and-126629.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 17 Aug 2014, 02:45, edited 2 times in total.
Renamed the topic, edited the question and added the OA.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 11 Aug 2011, 08:18
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KunalPratap wrote:
T can work laone and finishes job in 6 hours, P & J can do the same independently in 3 and 2 hours each. P starts working and after 1 hour P joins, both of them work for another 1 hour. After that J joins them and thet finish the job together. What was freaction of job done by P????

1) 1/9
2) 1/6
3) 1/3
4) 7/18
5) 4/9


Please correct your question. Who starts and who joins?
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 11 Aug 2011, 23:15
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1st hour T works = 1/6 work completed = 1/6 remaining work = 5/6

2nd hour T works = 1/6 work completed = 1/6 + 1/3 = 1/2 remaining work = 5/6-1/2 = 1/3

when (1/6+1/3+1/2) all 3 work, it is completed in 1 hr

hence remaining work is completed in 1/3 hr

now in 60 min T completes 1/6 work
in 1/3 = 20 min T completes 1/9 work

thus, 1/6 + 1/6 + 1/9 = 4/9.

hence E.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 12 Aug 2011, 11:15
amit2k9 wrote:
1st hour T works = 1/6 work completed = 1/6 remaining work = 5/6

2nd hour T works = 1/6 work completed = 1/6 + 1/3 = 1/2 remaining work = 5/6-1/2 = 1/3

when (1/6+1/3+1/2) all 3 work, it is completed in 1 hr

hence remaining work is completed in 1/3 hr

now in 60 min T completes 1/6 work
in 1/3 = 20 min T completes 1/9 work

thus, 1/6 + 1/6 + 1/9 = 4/9.

hence E.



I did the same for the first two periods, but then in the third, 1/3 hr is left * T's 1/6th = 1/18, thus 7/18 total.

What am I misunderstanding?
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 12 Aug 2011, 11:45
eragotte wrote:
amit2k9 wrote:
1st hour T works = 1/6 work completed = 1/6 remaining work = 5/6

2nd hour T works = 1/6 work completed = 1/6 + 1/3 = 1/2 remaining work = 5/6-1/2 = 1/3

when (1/6+1/3+1/2) all 3 work, it is completed in 1 hr

hence remaining work is completed in 1/3 hr

now in 60 min T completes 1/6 work
in 1/3 = 20 min T completes 1/9 work

thus, 1/6 + 1/6 + 1/9 = 4/9.

hence E.



I did the same for the first two periods, but then in the third, 1/3 hr is left * T's 1/6th = 1/18, thus 7/18 total.

What am I misunderstanding?


Same here. got D. Would be happy for an explanation if OA is E.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 13 Aug 2011, 16:02
First hour:

T: 1/6 job/hour * 1 hour = 1/6 job

Remaining work: 1 - 1/6 = 5/6 job

Second hour:

T: 1/6 job/hour * 1 hour = 1/6 job
P: 2/6 job/hour * 1 hour = 2/6 job

Remaining work: 5/6 - 3/6 = 2/6 job
T, P, J combined rate: 1 job/hour.
Remaining time to complete 2/6 job: 2/6 job / 1 job/hour = 2/6 hours

T: 1/6 job/hour * 2/6 hours = 2/36 = 1/18 jobs
P: 2/6 job/hour * 2/6 hours = 4/36 = 1/9 jobs
J: 3/6 job/hour * 2/6 hours = 6/36 = 1/6 jobs

Thus T completes 1/6 + 1/6 + 1/18 = (3 + 3 + 1)/18 = 7/18 of the job
P completes 2/6 + 1/9 = (6 + 2)/18 = 8/18 of the job
J completes 1/6 = 3/18 of the job

IMO:
[Reveal] Spoiler:
D
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 14 Aug 2011, 00:57
I too got 7/18. If T works for 1 hr and complete 1/6 work then in 20 minutes (1/3 of an hour) T can finish 1/3 of job that T does in 1 hr. So it should be 1/6*1/3=1/18. So total work done by T is:
1/6+1/6+1/18=7/18.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 30 Oct 2011, 10:49
I got 7/18 toooo
could anyone plz explain why the answer is 4/9??
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 31 Oct 2011, 22:01
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KunalPratap wrote:
T can work alone and will finish job in 6 hours, P & J can do the same independently in 3 and 2 hours each. T starts working alone and after 1 hour P joins, both of them work for another 1 hour. After that J joins them and they finish the job together. What was fraction of job done by T????

1) 1/9
2) 1/6
3) 1/3
4) 7/18
5) 4/9


T alone does the work in 6 hrs so rate = 1/6 work/hr
For P, the rate of work = 1/3 = 2/6 work/hr
For J, the rate of work = 1/2 = 3/6 work/hr
In first hour, T works alone so 1/6 of the work is done.
In the second hour, T and P work so 1/6 + 2/6 = 3/6 of the work is done. Now only 2/6 of the work is left.
In the third hour, they all work together at rate 1 work/hr (1/6+2/6+3/6)
Since only 2/6 of the work is left, time taken = 2/6 hr
Now, we know that T worked for the complete 2(2/6) hrs at the rate (1/6) so work done by T = (1/6)*2(2/6) = 7/18th of the entire work.

Answer is D.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 02 Nov 2011, 07:36
Use respective work rates, I got:

(1)*1/6 + (1)*(1/6+2/6) + x*(1/6+2/6+3/6) = 1 (1 whole job)

Solving for x: 4/6 + x = 1 -> x = 2/6 = 1/3

So T worked for a total of 1+1+1/3 = 7/3 hours at the rate of 1/6 jobs per hour.

So T completed 7/3 * 1/6 = 7/18 of one job. Answer is D.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 13 Nov 2011, 13:01
I too also got D 7/18
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 04 Jan 2012, 23:55
D should be the answer. E is wrong.
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 16 Aug 2014, 21:21
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Re: Tom, working alone, can paint a room in 6 hours. Peter and [#permalink] New post 17 Aug 2014, 02:53
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fluke wrote:
KunalPratap wrote:
T can work laone and finishes job in 6 hours, P & J can do the same independently in 3 and 2 hours each. P starts working and after 1 hour P joins, both of them work for another 1 hour. After that J joins them and thet finish the job together. What was freaction of job done by P????

1) 1/9
2) 1/6
3) 1/3
4) 7/18
5) 4/9


Please correct your question. Who starts and who joins?


The proper version of this question is below:
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 hour and has done 1/6*(t+2) part of the job;
Peter worked for t+1 hour 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:

1/6*(t+2)+1/3*(t+1)+1/2*t=1 --> multiply by 6 --> (t+2)+(2t+2)+3t=6 --> t=1/3;

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

Answer: E.

[color=#ff0000]OPEN DISCUSSION OF THIS QUESTION IS HERE: tom-working-alone-can-paint-a-room-in-6-hours-peter-and-126629.html
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Re: Tom, working alone, can paint a room in 6 hours. Peter and   [#permalink] 17 Aug 2014, 02:53
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