Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 21 seconds. The ratio of their speeds is? Choose one:  A) 3/7  B) 2/3  C) 3/5  D) 3/1  E) 3/3
Let the speeds of the two trains be x m/sec and y m/sec respectively. Then, length of the first train = 27 x meters, and length of the second train = 17 y meters. (27 x + 17 y) / (x + y) = 21   ==&gt; 27 x + 17 y = 21 x + 21 y ==&gt; 6 x = 4 y ==&gt; x/y   = 2/3.   Answer: 2/3
<result>B</result>
Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 21 seconds. The ratio of their speeds is?