In what ratio should a variety of rice costing Rs. 4.5 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 choice from the following options: A) 5 / 6 B) 5 / 9 C) 5 / 1 D) 5 / 3 E) 5 / 12

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 - 4.5 ) = 5 / 12 answer : e"
Answer: E