In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

[EX Q]: Problem: of the final grades received by the students in a certain math course , 1 / 5 are a ' s , 1 / 4 are b ' s , 1 / 2 are c ' s , and the remaining 30 grades are d ' s . what is the number of students in the course ? 
Options: a ) 80 , b ) 110 , c ) 160 , d ) 600 , e ) 400
[EX A]: d

[EX Q]: Problem: a sum of money lent out at s . i . amounts to a total of $ 480 after 2 years and to $ 680 after a further period of 5 years . what was the initial sum of money that was invested ? 
Options: a ) $ 360 , b ) $ 380 , c ) $ 400 , d ) $ 420 , e ) $ 440
[EX A]: c

[EX Q]: Problem: the positive numbers w , x , y , and z are such that x is 25 percent greater than y , y is 20 percent greater than z , and w is 20 percent less than x . what percent greater than z is w ? 
Options: a ) 15.2 % , b ) 16.2 % , c ) 20.0 % , d ) 23.2 % , e ) 24.8 %
[EX A]:
b