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Maintenance work Q2

jwednesday

New member
Joined
Dec 10, 2009
Messages
16
Bob can do a certain maintenance job in 1.5 hours. It takes Jim 2.5 hours to do the same job. Bob had been working on the job for half an hour when he was called to a more important job and Jim took over. How many hours did it take Jim to finish the job?

I think it goes as follows ... Bob x - 0.5 over 1.5 Jim is x over 2.5

1.5 (x - 0.5) + x = 1 1.5x - 1.125 + 1.2x = 3 2.7x = 4.125 x = 1.527
-------------- --- --------------- --------- --- ------ -------
1.5 2.5 1.5 2.5 3 2.7 2.7


Not sure I did this right the answer is suppose to be 1 and 2/3 hours
 

chrisr

Full Member
Joined
Nov 29, 2009
Messages
355
How much of the job does Bob get done in the first half hour, if it takes him 3/2 hours to complete the job?
A third.
Therefore, Jim has to complete 2/3 of the job.
How long does it take him to do 1/3 of the job?
2.5/3 hours.

So how long will it take him to finish?
 

jwednesday

New member
Joined
Dec 10, 2009
Messages
16
the answer is 1 and 2/3 ... I get close to the answer but not the exact ... did I do this right?
 

chrisr

Full Member
Joined
Nov 29, 2009
Messages
355
You may need to quietly study how to develop this type of formula.

Bob works for half an hour, so there is 1-(0.5)/(1.5) of the job left for Jim to complete.

0.5/1.5 is the fraction of the job that Bob completed,
so "1-that" is the fraction left.

Jim does 1/(2.5) of the job per hour, since he takes 2.5 hours by himself.

He does 1-{(0.5)/(1.5)} of the job in x hours.

Therefore x/2.5 = 1-{0.5/1.5},
which is x/2.5 = 1-(1/3) = 2/3
so x = (2.5)2/3 hours
 

jwednesday

New member
Joined
Dec 10, 2009
Messages
16
you got an answer of 2.5 2/3 but the answer is suppose to be 1 2/3.
 

wjm11

Senior Member
Joined
Nov 13, 2004
Messages
1,417
you got an answer of 2.5 2/3 but the answer is suppose to be 1 2/3.
No.

Chris did not say that.

What he said was:

x = (2.5)2/3 hours

The parentheses mean multiplication:

x = (2.5)2/3 hours = (5/2)(2/3) = 5/3 = 1 2/3

Please go back and study his entire explanation until you understand it.
 

jwednesday

New member
Joined
Dec 10, 2009
Messages
16
sorry, I miss understood
 
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