If 10 litres of an oil of Rs.50 per litres be mixed with 5 litres of another oil of Rs.68 per litre then what is the rate of mixed oil per litre? Choose the correct choice.
A) rs . 49.17  B) rs . 51.03  C) rs . 56  D) rs . 55.33  E) none of the above

Rationale: "50 * 10 = 500 68 * 5 = 340 840 / 15 = 56 answer : c"
Answer: C