The cost of 3 pens and 5 pencils is Rs.100. Also the cost of one pen and one pencil is in the ratio of 5:1 respectively. What is the cost of one dozen pens?	Choose the correct choice from the following: A) rs . 200 B) rs . 250 C) rs . 300 D) rs . 150 E) none of these

Rationale: "explanation : let the cost of one pen is ‘ 5 x ’ and pencil is ‘ x ’ 3 x 5 x + 5 x = rs . 100 15 x + 5 x = rs . 100 x = 100 / 20 = 5 : . cost of 1 pen = 5 x = 5 x 5 = 25 : . cost of 12 pens , i . e . ( one dozen ) = 25 x 12 = rs . 300 answer : option c"
Answer: C