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'.

[EX Q]: Problem: what will be the difference between simple and compound interest @ 20 % per annum on a sum of $ 500 after 2 years ? 
Options: a ) $ 10 , b ) $ 20 , c ) $ 25 , d ) $ 30 , e ) $ 40
[EX A]: b

[EX Q]: Problem: a reduction of 50 % in the price of apples would enable a man to obtain 50 more for rs . 50 , what is reduced price per dozen ? 
Options: a ) 1 , b ) 3 , c ) 6 , d ) 7 , e ) 10
[EX A]: c

[EX Q]: Problem: if 15 % of 30 % of 50 % of a number is 90 , then what is the number ? 
Options: a ) 4000 , b ) 3050 , c ) 4400 , d ) 4500 , e ) none of these
[EX A]:
a