Task: Question Answering
Input (English): Problem: in what ratio should a variety of rice costing rs . 20 per kg be mixed with another variety of rice costing rs . 31.50 per kg to obtain a mixture costing rs . 23.75 per kg ? 
Options: a ) 16 : 30 , b ) 30 : 14 , c ) 16 : 31 , d ) 31 : 15 , e ) 15 : 31
Output (English): d