In what ratio should a variety of Rice costing Rs. 7 per kg be mixed with another variety of Rice costing Rs. 14.50 per kg to obtain a mixture costing Rs. 9.75 per kg?
Choose the correct answer
A) 19 : 10 B) 19 : 11 C) 11 : 19 D) 12 : 18 E) 11 : 20

Rationale: "let us say the ratio of the quantities of cheaper and dearer varieties = x : y by the rule of allegation , x / y = ( 14.50 - 9.75 ) / ( 9.75 - 7 ) = 31 / 15 answer : b"
Answer: B