Problem: a can do a piece of work in 8 days and b alone can do it in 12 days . how much time will both take to finish the work ?
Rationale: "this question can be solved by different methods . we need to conserve time in exams so solving this problem using equations is the good idea . time taken to finish the job = xy / ( x + y ) = 8 x 12 / ( 8 + 12 ) = 96 / 20 = 4.8 days answer : a"
annotated_formula: divide(const_1, add(divide(const_1, 8), divide(const_1, 12)))