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'.

[EX Q]: Problem: a river boat leaves silver town and travels upstream to gold town at an average speed of 6 kilometers per hour . it returns by the same route at an average speed of 5 kilometers per hour . what is the average speed for the round - trip in kilometers per hour ? 
Options: a ) 5.5 , b ) 7.1 , c ) 7.2 , d ) 7.0 , e ) 8.0
[EX A]: a

[EX Q]: Problem: mary can do a piece of work in 28 days . rosy is 40 % more efficient than mary . the number of days taken by rosy to do the same piece of work is ? 
Options: a ) 22 , b ) 24 , c ) 20 , d ) 25 , e ) 27
[EX A]: c

[EX Q]: Problem: if 7 cats can kill 7 rats in 7 minutes , how long will it take 100 cats to kill 100 rats ? 
Options: a ) 5 minutes , b ) 6 minutes , c ) 7 minutes , d ) 8 minutes , e ) 9 minutes
[EX A]:
c