Problem: a can do a piece of work in 5 days and b can do it in 4 days how long will they both work together to complete the work ?
Rationale: "explanation : a ’ s one day work = 1 / 5 b ’ s one day work = 1 / 4 ( a + b ) ’ s one day work = 1 / 5 + 1 / 4 = 9 / 20 = > time = 20 / 9 = 2 2 / 9 days answer : option d"
annotated_formula: divide(const_1, add(divide(const_1, 5), divide(const_1, 4)))