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'.

[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
[A]: b


[Q]: Problem: if a large pizza has a radius that is 10 % larger that that of a medium pizza , what is the percent increase in area between a medium and a large pizza ? 
Options: a ) 15 % , b ) 21 % , c ) 25 % , d ) 30 % , e ) 36 %
[A]: b


[Q]: Problem: if it is assumed that 80 percent of those who receive a questionnaire by mail will respond and 300 responses are needed , what is the minimum number of questionnaires that should be mailed ? 
Options: a ) 375 , b ) 420 , c ) 480 , d ) 500 , e ) 600
[A]:
a