Two trains of equal lengths take 10 sec and 15 sec, respectively, to cross a telegraph post. If the length of each train is 120 m, in what time will they cross each other, travelling in opposite directions?
Choose the correct choice from the following answers:
A) 17 sec
B) 12 sec
C) 18 sec
D) 19 sec
E) 52 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 is 120 m, in what time will they cross each other, travelling in opposite directions?