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A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo

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A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 18 Aug 2010, 09:35
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A can do a job in 12 hrs B can do a job in 6 hours. If A and B work for 3 hours , how many hours will it take A to finsih the rest of the job
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Re: A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 18 Aug 2010, 09:49
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rxs0005 wrote:
A can do a job in 12 hrs B can do a job in 6 hours. If A and B work for 3 hours , how many hours will it take A to finsih the rest of the job



Answer: A would finish the job in 3 hours time.

In 3 hours, A would complete 1/4th of the job and B would complete 1/2 of the job.

Hence total job completed in 3 hours is 3/4th.

Rest 1/4 would be completed by A in 3 hours.
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A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 22 Aug 2017, 08:16
rxs0005 wrote:
A can do a job in 12 hrs B can do a job in 6 hours. If A and B work for 3 hours , how many hours will it take A to finsih the rest of the job

A's rate is \(\frac{1job}{12hrs}\)

B's rate is \(\frac{1job}{6hrs}\)

They work together for three hours; add their rates.

\(\frac{1}{12}\) + \(\frac{1}{6}\) = \(\frac{1}{4}\)

\(rt=W\) is the work they will finish in 3 hours:

\(\frac{1}{4}\)* 3 = \(\frac{3}{4}\) of the job (work) is finished.

A will finish the remaining \(\frac{1}{4}\)W in \(W/r= t\):

\(\frac{\frac{1}{4}}{\frac{1}{12}}\) = 3 hours for A to finish the rest of the work
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Re: A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 22 Aug 2017, 08:45
rxs0005 wrote:
A can do a job in 12 hrs B can do a job in 6 hours. If A and B work for 3 hours , how many hours will it take A to finsih the rest of the job


Let the total work be 12 units

Efficiency of A = 1 unit/hr
Efficiency of B = 2 unit/hr

Combined Efficiency of A & B = 3 unit/hr

Quote:
If A and B work for 3 hours


Work completed is 3*3 = 9 units , work remaining is 3 units.

So, A will complete the remaining work in 3 hours.
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Re: A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 23 Aug 2017, 00:45
All the solutions appear to me as \\ frac {1} like this type it is not clearly legible what to do

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Re: A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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Re: A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 24 Aug 2017, 16:06
rxs0005 wrote:
A can do a job in 12 hrs B can do a job in 6 hours. If A and B work for 3 hours , how many hours will it take A to finsih the rest of the job


We can let the rate of A = 1/12, the rate of B = 1/6, the time of A = t + 3 (where t is the number of hours it takes A to finish the rest of the job), and the time of B = 3. Thus:

(1/12)(t + 3) + (1/6)3 = 1

(t + 3)/12 + 1/2 = 1

(t + 3)/12 = 1/2

Multiplying by 12, we have:

t + 3 = 6

t = 3
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A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 27 Aug 2017, 03:16
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guys today i will show you a way to solve word problems which avoids fractions and tedious calculations which can help you solve hard complex problems in 90 secs. I have used it in gmat and it saved me a lot of time

for this sum
assume the job as 24 ( this number can be any lcm of the time take)
rate for a =24/12
= 2 units/hr
rate for b = 24/6
= 4 units/hr
if a and b work for 3 hrs together rate is 2+4=6
work done is 6*3=18 units
work left is 24-18=6 units
time taken by a to finish the job is 6/2=3
hence answer is 3

this approach can be applied to any sum of work rate . it gives fast results only assumption is the unit of work. For a sum to fill water in a tank you assume the capacity of tank
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Re: A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 16 Nov 2017, 23:02
Bunuel wrote:
subham0001 wrote:
All the solutions appear to me as \\ frac {1} like this type it is not clearly legible what to do

Sent from my XT1022 using GMAT Club Forum mobile app


Which browser are you using? Have you tried reloading?

I am using the app but on browser its okay.

Sent from my XT1022 using GMAT Club Forum mobile app
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A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo  [#permalink]

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New post 07 Aug 2019, 03:50
Let total job be 24 units.

Efficiency of A = 24/12 = 2 units per hour
Efficiency of B = 24/6 = 4 units per hour
Job completed by A in 3 hours = 2 x 3 = 6 units
Job completed by B in 3 hours = 4 x 3 = 12 units
Total Job completed = 18 units
Balance (leftover) = 24-18 =6 units.
At A's current efficiency of 2 units per hour, the rest of the job will be completed in 3 hours [6 units/(2 units/hour)]
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A can do a job in 12 hrs B can do a job in 6 hours. If A and B work fo   [#permalink] 07 Aug 2019, 03:50
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