## Elementary and Intermediate Algebra: Concepts & Applications (6th Edition)

We add the rates of the two machines to find their overall rate: $$\frac{1}{20}+\frac{1}{30}\\ \frac{3}{60}+\frac{2}{60}\\ \frac{5}{60}\\ \frac{1}{12}$$ Thus, taking the reciprocal, it would take them 12 minutes to do it together.