Task: Question Answering
Input (English): Problem: a can do a job in 15 days and b can do it in 30 days . a and b working together will finish twice the amount of work in days ? 
Options: a ) 20 , b ) 22 1 / 2 , c ) 22 1 / 0 , d ) 22 1 / 9 , e ) 22 1 / 1
Output (English): a