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 can do a piece of work in 12 days . he worked for 15 days and then b completed the remaining work in 10 days . both of them together will finish it in . 
Options: a ) 12 1 / 2 days , b ) 10 1 / 2 days , c ) 12 1 / 3 days , d ) 10 1 / 3 days , e ) 11 1 / 2 days

A: a
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Q: Problem: an engine moves at the speed of 60 kmph without any coaches attached to it . speed of the train reduces at the rate that varies directly as the square root of the number of coaches attached . when 4 coaches are attached speed decreases to 48 kmph . what will be the speed of train when 36 coaches are attached . 
Options: a ) 24 , b ) 28 , c ) 20 , d ) 32 , e ) 40

A: a
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Q: Problem: speed of a boat in standing water is 16 kmph and the speed of the stream is 2 kmph . a man rows to a place at a distance of 7740 km and comes back to the starting point . the total time taken by him is : 
Options: a ) 914.2 hours , b ) 900 hours , c ) 915 hours , d ) 982.9 hours , e ) 915 hours

A:
d
****