Two trains of equal lengths take 12 sec and 24 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) 18 sec
B) 12 sec
C) 17 sec
D) 21 sec
E) 16 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= 120/24= 
<gadget id="calculator">120/24</gadget>
<output>5</output>
5 m/sec.   Relative speed= 10 + 5= 
<gadget id="calculator">10 + 5</gadget>
<output>15</output>
15 m/sec.   Required time= (120 + 120)/15= 
<gadget id="calculator">(120 + 120)/15</gadget>
<output>16</output>
16 sec.   Answer: 16 sec
<result>E</result>
Two trains of equal lengths take 12 sec and 24 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?