In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Problem: how many liters of water must be evaporated from 50 liters of a 2 - percent sugar solution to get a 10 - percent solution ? 
Options: a ) 25 , b ) 30 , c ) 35 , d ) 40 , e ) 45
d

Problem: in one hour , a boat goes 8 km along the stream and 2 km against the stream . the sped of the boat in still water ( in km / hr ) is : 
Options: a ) 3 , b ) 5 , c ) 8 , d ) 9 , e ) 10
b

Problem: john had a stock of 1300 books in his bookshop . he sold 75 on monday , 50 on tuesday , 64 on wednesday , 78 on thursday and 135 on friday . what percentage of the books were not sold ? 
Options: a ) 50.4 % , b ) 23.8 % , c ) 66.5 % , d ) 69.0 % , e ) 43.5 %

d