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 is two years older than b who is twice as old as c . if the total of the ages of a , b and c be 12 , the how old is b ?
Options: a ) 10 years , b ) 4 years , c ) 6 years , d ) 15 years , e ) 16 years
[EX A]: b

[EX Q]: Problem: each of the positive integers a and c is a 4 - digit integer . if each of the digits 0 through 9 appears in one of these 3 integers , what is the maximum possible value of the sum of a and c ?
Options: a ) 18695 , b ) 18325 , c ) 18365 , d ) 18395 , e ) 18485
[EX A]:
d