In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Q: Problem: a water tank is four - fifths full . pipe a can fill a tank in 10 minutes and pipe b can empty it in 6 minutes . if both the pipes are open , how many minutes will it take to empty or fill the tank completely ? 
Options: a ) 6 , b ) 9 , c ) 10 , d ) 12 , e ) 15

A: d
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Q: Problem: a and b can do a piece of work in 3 days , b and c in 4 days , c and a in 6 days . how long will c take to do it ? 
Options: a ) 33 , b ) 77 , c ) 24 , d ) 55 , e ) 71

A: c
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Q: Problem: the amounts of time that three secretaries worked on a special project are in the ratio of 2 to 3 to 5 . if they worked a combined total of 80 hours , how many hours did the secretary who worked the longest spend on the project ? 
Options: a ) 80 , b ) 70 , c ) 56 , d ) 16 , e ) 40

A:
e
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