Problem: a can do a piece of work 60 days . b can do work in 90 days . in how many days they will complete the work together ?
Rationale: lcm = 180 , ratio = 60 : 90 = 2 : 3 no of days = 180 / ( 2 + 3 ) = 180 / 5 = 36 days answer : a
annotated_formula: divide(const_1, add(divide(const_1, 60), divide(const_1, 90)))