Task: Question Answering
Input (English): Problem: the average age of a group of persons going for picnic is years . fifteen new persons with an average age of 15 years join the group on the spot due to which their average age becomes 15.5 years . the number of persons initially going for picnic is 
Options: a ) 5 , b ) 10 , c ) 15 , d ) 40 , e ) 50
Output (English): c