![Woody Calculus introduction to differential-equation mixing problems, showing a perfectly stirred saltwater tank with inflow and outflow. The governing model is Q′(t) = c_in r_in − [Q(t)/V(t)]r_out. Equal flow rates produce constant volume, while unequal flow rates produce changing volume.](https://k3p6r8v3.delivery.rocketcdn.me/wp-content/uploads/2026/08/Mixing_Problems_Slide_01.png)
Learn how to model and solve differential-equation mixing problems with rate in minus rate out. Work through constant-volume, draining-tank, and overflow examples, then practice the complete seven-step method.
This full-length Woody Calculus web edition presents Brian M. Woody’s paper, The Golden Oscillator: Rhythmic Optimization in Natural Systems, preserving the original December 12, 2025 record date while adapting the work for clear mathematical web presentation.