Task: Question Answering
Input (English): Problem: the average marks obtained by 100 candidates in an examination is 50 . find how many candidates have passed in the examination , if the average marks of candidates who passed is 70 and that of failed candidates is 20 . 
Options: a ) 33 , b ) 77 , c ) 60 , d ) 29 , e ) 11
Output (English): c