Two trains of equal lengths take 12 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:
A) 22	B) 13	C) 77	D) 99	E) 21
Speed of the first train = 120/12= 
<gadget id="calculator">120/12</gadget>
<output>10</output>
10 m/sec.   Speed of the second train= 120/15= 
<gadget id="calculator">120/15</gadget>
<output>8</output>
8 m/sec.   Relative speed= 10 + 8= 
<gadget id="calculator">10 + 8</gadget>
<output>18</output>
18 m/sec.   Required time= (120 + 120)/18 = 13 sec.   Answer: 13
<result>B</result>
Two trains of equal lengths take 12 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?