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?	Choose the correct choice from the following answers
A) 11
B) 18
C) 12
D) 99
E) 13
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
<result>C</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?