Task: Question Answering
Input (English): Problem: a is 30 % more efficient than b . how much time will they , working together , take to complete a job which a alone could have done in 23 days ? 
Options: a ) 11 days , b ) 13 days , c ) 20 3 / 17 days , d ) 21 days , e ) none of these
Output (English): b