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 20 seconds . the ratio of their speeds is ?
"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 ) = 20 = = > 27 x + 17 y = 20 x + 20 y = = > 7 x = 3 y = = > x / y = 3 / 7 . answer : a"
divide(subtract(27, 20), subtract(20, 17))