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Work Rate

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Work Rate

by jainrahul1985 » Sun Jul 26, 2009 9:27 am
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?
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by shibal » Sun Jul 26, 2009 9:36 am
would it be 7/18?
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by jainrahul1985 » Sun Jul 26, 2009 9:42 am
Sorry , I don't have answer . How did you solve it ?
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by shibal » Sun Jul 26, 2009 9:56 am
since A does it in 6 hrs, B in 3 and C in 2... i fixed an amount as the 'work rate'.... 18.
so pr hour a does 1/6 of the job, b 1/3 and c 1/2.

after a working alone, we still have 15 to be done
b+a= 9, so we have 6 left
a+b+c=18

if they do 18 in an hour, they will do 6 in 20min.

so b has workd 6hrs with a and with the others 2

6+2/18= 4/9

not 7/18 as i had said before....
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by b2eby » Mon Jul 27, 2009 9:29 am
We know the respective rates for Tom, Peter, and John.
Tom: 1/6 Job/Hr
Peter: 1/3 Job/Hr
John: 1/2 Job/Hr

First Hour:
Tom Completes 1/6 of the Job

Second Hour:
Tom Completes 1/6 of the Job
Peter Completes 1/3 of the Job

What fraction of the job must still be completed?
1 - (1/6 - 1/6 - 2/6) = 1/3

Peter's share of this fraction (all three are working together):
(1/3) / (1/3 + 1/6 + 1/2) = 1/3

Peter's fraction of the whole job:
1/3 + (1/3)(1/3)
= 4/9
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by PussInBoots » Mon Jul 27, 2009 9:41 pm
We know the respective rates for Tom, Peter, and John.
Tom: 1/6 Job/Hr
Peter: 1/3 Job/Hr
John: 1/2 Job/Hr

First Hour:
Tom Completes 1/6 of the Job.

Second Hour:
Tom Completes 1/6 of the Job
Peter Completes 1/3 of the Job

What fraction of the job must still be completed?
1 - (1/6 - 1/6 - 2/6) = 1/3

How long does it take for three of them to finish the job?
1/6 + 1/3 + 1/2 = (1/3) / x
1 = 1/3 / x => x= 1/3

Peter's share = 1/3 + 1/3 * 1/3 = 4/9
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by MakeitHappen » Mon May 03, 2010 7:10 pm
I didnt understand how the below was arrived at:
what is x referring to?
PussInBoots wrote:
How long does it take for three of them to finish the job?
1/6 + 1/3 + 1/2 = (1/3) / x
1 = 1/3 / x => x= 1/3

Peter's share = 1/3 + 1/3 * 1/3 = 4/9
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by harshavardhanc » Tue May 04, 2010 4:17 am
jainrahul1985 wrote: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?
%ages and fractions.


T completes 16.66% in one hour, P completes 33.33% in one hour, and J completes 50% in one hour.

one hour after T starts, work done = 16.66%

T and P can complete (16.66 + 33.33) = 50% in one hour, so after two hours total work done = 50 + 16.66 = 66.66%

work remaining = 33.33% or 1/3rd.


together T,P, and J can complete 100% in one hour.

So, time required to complete 1/3 of the work = 1/3 hours. In these 1/3 hours, P will complete 1/3 *1/3 = 1/9th of the work.


therefore, total work done by P = 1/3 (in the second hour) + 1/9 (in the third hour)= 4/9.
Regards,
Harsha
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by debmalya_dutta » Tue May 04, 2010 4:32 am
T can finish in 1/6 of the room in 1 hr
P can finish in 1/3 of the room in 1 hr
J can finish in 1/2 of the room in 1 hr

After tom works for 1 hour, 1/6th of the painting is completed and remainder is 5/6th
Tom and P working together can finish (1/6 + 1/3) or 3/6th of the room in 1 hour and hence 2/6th of the painting remains
Tom, Pete & John working together can finish the complete room in (1/6+1/3+1/2) in an hour. So 2/6th or 1/3rd of the room can be completed in 1/3 hours.
Pete hence does 1/3 * 1/3 part working with the other 2

Total work that peter does = 1/3*1/3 + 1/3 = 1/9+1/3 = 4/9
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