Task: Question Answering
Input (English): Problem: in what ratio must a grocer mix two varieties of pulses costing rs . 15 and rs . 20 per kg respectively so as to get a mixture worth rs . 16.50 per kg ? 
Options: a ) 3 : 7 , b ) 5 : 7 , c ) 7 : 3 , d ) 7 : 5 , e ) none
Output (English): c