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'.

Example Input: Problem: ages of two sisters differ by 9 years . if 5 years ago , the elder one was twice as old the younger one , find their present age 
Options: a ) 1228 , b ) 1423 , c ) 1632 , d ) 1834 , e ) 1932
Example Output: b

Example Input: Problem: for any positive integer n , the sum of the first n positive integers equals n ( n + 1 ) / 2 . what is the sum of all the integers between 1 and 50 ? 
Options: a ) 1275 , b ) 1542 , c ) 985 , d ) 1024 , e ) 1125
Example Output: a

Example Input: Problem: in a school with 5 classes , each class has 2 students less than the previous class . how many students are there in the largest class if the total number of students at school is 115 ? 
Options: a ) 25 , b ) 26 , c ) 27 , d ) 28 , e ) 29
Example Output:
c