In what ratio should a variety of rice costing Rs. 6.5 per kg be mixed with another variety of rice costing Rs. 8.75 per kg to obtain a mixture costing Rs. 7.50 per kg?	Choose the correct answer:  A) 5 / 6  B) 5 / 9  C) 5 / 4  D) 5 / 3  E) 7 / 6

Rationale: "let us say the ratio of the quantities of cheaper and dearer varieties = x : y by the rule of allegation , x / y = ( 8.75 - 7.50 ) / ( 7.50 - 6.5 ) = 5 / 4 answer : c"
Answer: C