Two trains of equal lengths take 10 sec and 15 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?	Select:
A) 16 sec
B) 12 sec
C) 17 sec
D) 21 sec
E) 23 sec
Speed of the first train = 120/10= 
<gadget id="calculator">120/10</gadget>
<output>12</output>
12 m/sec.   Speed of the second train= 120/5 = 8 m/sec.   Relative speed = 12 + 8= 
<gadget id="calculator">12 + 8</gadget>
<output>20</output>
20 m/sec.   Required time= (120 + 120)/20= 
<gadget id="calculator">(120 + 120)/20</gadget>
<output>12</output>
12 sec.   Answer: 12 sec
<result>B</result>
Two trains of equal lengths take 10 sec and 15 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?