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Help solving a work problem..should be easy?

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Help solving a work problem..should be easy?

by gen3hatch » Sun Nov 22, 2009 1:50 pm
Pumps A, B, C operate at their respective costant rates. Pump A & B operating simultaneously can fll a certain tank in 6/5 hour; pumps A &C can fill a tank simultaneously in 3/2 hour and pump B & C operating simultaneously can fill a tank in 2 hours. How many hours does it take pump A, B, & C operting simultaneously to fill the tank?
A 1/3
B 1/2
C 2/3
D 5/6
E 1

Can you show the work and calculations behind the answer?
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by ershovici » Mon Nov 23, 2009 1:51 am
From the question we have three different equotions:
1/A+1/B=6/5 - A+B=5/6
1/A+1/C=3/2 - A+C=2/3
1/B+1/C=2 - B+C=1/2

Add this equptions: 2A+2B+2C=12/6 = 2
2(A+B+C)=2
A+B+C = 1

I THINK ANSWER IS E
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by gen3hatch » Mon Nov 23, 2009 10:04 am
Yes. your right..Thanks!
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by heshamelaziry » Mon Nov 23, 2009 10:34 am
ershovici wrote:From the question we have three different equotions:
1/A+1/B=6/5 - A+B=5/6
1/A+1/C=3/2 - A+C=2/3
1/B+1/C=2 - B+C=1/2

Add this equptions: 2A+2B+2C=12/6 = 2
2(A+B+C)=2
A+B+C = 1

I THINK ANSWER IS E

When the questionn says A and B can do a job in 6/5 doesn't it mean that to get to 6/5 we did ------> 1/a + 1/b = 5/6 so A + B = 6/5 ?

I am confused we usually do 1/A + 1/B = 5/6 and then take the reciprocal of 5/6 to get the total time taken by A and B to do one job , so it should be A + B = 6/5


Please help :(
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by aspirant1 » Mon Nov 23, 2009 10:57 am
consider work = time x rate
for A+B , time 6/5 hrs

rate A+B = Work/ time; 1/(6/5) = 5/6
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