Task: Question Answering
Input (English): Problem: a work as fast as b . if b can complete a work in 20 days independently , the number of days in which a and b can together finish the work in ? 
Options: a ) 2 days , b ) 3 days , c ) 4 days , d ) 5 days , e ) 6 2 / 3 days
Output (English): e