Two trains of equal lengths take 12 sec and 20 sec respectively to cross a telegraph post. If the length of each train be 120 m, in what time will they cross other travelling in opposite direction? Choices:	A) 17 sec	B) 15 sec	C) 16 sec	D) 11 sec	E) 18 sec
Speed of the first train = 120/12= 
<gadget id="calculator">120/12</gadget>
<output>10</output>
10 m/sec.   Speed of the second train= 120/20= 
<gadget id="calculator">120/20</gadget>
<output>6</output>
6 m/sec.   Relative speed= 10 + 6= 
<gadget id="calculator">10 + 6</gadget>
<output>16</output>
16 m/sec.   Required time= (120 + 120)/16= 
<gadget id="calculator">(120 + 120)/16</gadget>
<output>15</output>
15 sec.   Answer:15 sec
<result>B</result>
Two trains of equal lengths take 12 sec and 20 sec respectively to cross a telegraph post. If the length of each train be 120 m, in what time will they cross other travelling in opposite direction?