Task: Question Answering
Input (English): Problem: in what ratio must water be mixed with milk to gain 16 2 / 3 % on selling the mixture at cost price ? 
Options: a ) 1 : 9 , b ) 1 : 1 , c ) 1 : 2 , d ) 1 : 6 , e ) 1 : 5
Output (English): d