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5) how hard do these machines work?

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5) how hard do these machines work?

by ern5231 » Fri Apr 30, 2010 10:34 pm
Two machines A and B drain water from a tank. A worked alone for 4 hours to
Drain half of the water in the tank. Then, B joined and the remaining water could be drained in 3 hours. In how many hours could B drain the water alone?


I picked up this question from net. Don't have the options. I worked out the answer 24. Wts your opinion?
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by beat_gmat_09 » Fri Apr 30, 2010 11:00 pm
ern5231 wrote:Two machines A and B drain water from a tank. A worked alone for 4 hours to
Drain half of the water in the tank. Then, B joined and the remaining water could be drained in 3 hours. In how many hours could B drain the water alone?


I picked up this question from net. Don't have the options. I worked out the answer 24. Wts your opinion?
1/4+1/x=1/3
x=12 B can drain half water in 12 hrs therefore alone it can drain in 24 hrs.
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by harshavardhanc » Sat May 01, 2010 3:31 am
ern5231 wrote:Two machines A and B drain water from a tank. A worked alone for 4 hours to
Drain half of the water in the tank. Then, B joined and the remaining water could be drained in 3 hours. In how many hours could B drain the water alone?


I picked up this question from net. Don't have the options. I worked out the answer 24. Wts your opinion?
A can drain half of the quantity in 4 hrs i.e 25% in one hour.

together with B, he's able to drain half the water in 3 hrs, i.e efficiency is increased to 33.33% or by 8.33%. which is 1/12.

hence, B can drain half the tank in 12 hours or full capacity of the tank in 24 hours.
Regards,
Harsha
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by this_time_i_will » Sat May 01, 2010 6:02 am
ern5231 wrote:Two machines A and B drain water from a tank. A worked alone for 4 hours to
Drain half of the water in the tank. Then, B joined and the remaining water could be drained in 3 hours. In how many hours could B drain the water alone?


I picked up this question from net. Don't have the options. I worked out the answer 24. Wts your opinion?
A simple formula that can be handy for any similar type of problem is:

(A+B) togethar = AB/(A+B) .
6 = 8B/(8+B)
B = 24.
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