Problem: a train speeds past a pole in 10 seconds and a platform 50 m long in 20 seconds . its length is :
Rationale: "let the length of the train be x meters and its speed be y m / sec . they , x / y = 10 = > y = x / 10 x + 50 / 20 = x / 10 x = 50 m . answer : option d"
annotated_formula: multiply(50, subtract(const_2, const_1))