The cost of 3 pens and 5 pencils is Rs.150. 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 choices.
A) Rs.200  B) Rs.250  C) Rs.300  D) Rs.450  E) None of these
Explanation:   Let the cost of one pen is ‘5x’ and pencil is ‘x’   3 X 5x + 5x = Rs.150   15x + 5x = Rs.150   X = 150/20= 
<gadget id="calculator">150/20</gadget>
<output>15/2 = around 7.5</output>
7.50   :. Cost of 1 pen= 5x = 5 x 7.50 = 37.50   :. Cost of 12 pens, i.e. (one dozen) = 37.50x 12 = Rs.450   Answer: Option Rs.450
<result>D</result>
The cost of 3 pens and 5 pencils is Rs.150. 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?