The cost of 3 pens and 5 pencils is Rs.260. 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? Options:
A) Rs.200	B) Rs.250	C) Rs.300	D) Rs.780	E) None of these
Explanation:   Let the cost of one pen is ‘5x’ and pencil is ‘x’   3 X 5x + 5x = Rs.260   15x + 5x = Rs.260   X = 260/20= 
<gadget id="calculator">260/20</gadget>
<output>13</output>
13   :. Cost of 1 pen= 5x = 5 x 13 = 65   :. Cost of 12 pens, i.e. (one dozen) = 65 x 12 = Rs.780   Answer: Option Rs.780
<result>D</result>
The cost of 3 pens and 5 pencils is Rs.260. 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?