Two trains of equal lengths take 15 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?  Choose the correct choice from the following options:
A) 16 sec
B) 12 sec
C) 17 sec
D) 21 sec
E) 23 sec
Speed of the first train = 120/15= 
<gadget id="calculator">120/15</gadget>
<output>8</output>
8 m/sec.   Speed of the second train= 120/20= 
<gadget id="calculator">120/20</gadget>
<output>6</output>
6 m/sec.   Relative speed= 8 + 6= 
<gadget id="calculator">8 + 6</gadget>
<output>14</output>
14 m/sec.   Required time= (120 + 120)/14 = 17 sec.   Answer: 17 sec
<result>C</result>
Two trains of equal lengths take 15 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?