Problem: a is twice as fast as b . if b alone can do a piece of work in 18 days , in what time can a and b together complete the work ?
Rationale: "a can do the work in 18 / 2 i . e . , 9 days . a and b ' s one day ' s work = 1 / 9 + 1 / 18 = ( 2 + 1 ) / 18 = 1 / 6 so a and b together can do the work in 6 days . answer : d"
annotated_formula: inverse(add(divide(const_1, 18), multiply(divide(const_1, 18), const_2)))