Two trains of equal lengths take 5 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? Options:  A) 22  B) 12  C) 7.5  D) 99  E) 21
Speed of the first train = 120/5= 
<gadget id="calculator">120/5</gadget>
<output>24</output>
24 m/sec.   Speed of the second train= 120/15= 
<gadget id="calculator">120/15</gadget>
<output>8</output>
8 m/sec.   Relative speed= 24 + 8= 
<gadget id="calculator">24 + 8</gadget>
<output>32</output>
32 m/sec.   Required time= (120 + 120)/32= 
<gadget id="calculator">(120 + 120)/32</gadget>
<output>15/2 = around 7.5</output>
7.5 sec.   Answer: 7.5
<result>C</result>
Two trains of equal lengths take 5 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?