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Director  Joined: 07 Jun 2004
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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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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
Senior Manager  Status: Time to step up the tempo
Joined: 24 Jun 2010
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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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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.
Senior SC Moderator V
Joined: 22 May 2016
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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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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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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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Intern  Joined: 21 Aug 2017
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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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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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subham0001 wrote:
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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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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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

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
Intern  Joined: 21 Aug 2017
Posts: 3
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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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

I am using the app but on browser its okay.

Sent from my XT1022 using GMAT Club Forum mobile app
Manager  B
Joined: 04 Feb 2018
Posts: 51
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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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)] 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, 02:50

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