a train speeds past a pole in 20 seconds and a platform 100 m long in 25 seconds . its length is ?
"let the length of the train be x meters and its speed be y m / sec . they , x / y = 20 = > y = x / 20 x + 100 / 25 = x / 20 x = 400 m . answer : e"
multiply(100, subtract(const_2, const_1))