Task: Question Answering
Input (English): Problem: the ratio of boarders to day students at a school was originally 2 to 5 . however , after a number of new boarders join the initial 120 boarders , the ratio changed to 1 to 2 . if no boarders became day students and vice versa , and no students left the school , how many new boarders joined the school ? 
Options: a ) 30 , b ) 50 , c ) 70 , d ) 80 , e ) 90
Output (English): a