An analytical method for teaching students how to find the minimum liquid flowrate in rich-phase gas-absorption problems. The analytical solution is found by deriving explicit analytical expressions for the location and slope of the operating line in terms of only one variable, and then solving for the liquid flowrate that gives only one point of intersection with the equilibrium line. This can be used alongside the more traditional graphical method that requires students to convert the concentrations into solute-free ratios. Students seem to find this method easy to understand and it is well suited for use in computer packages. The method is limited to cases where an analytical expression for the equilibrium line is known and can be assumed constant along the length of the column (i.e., isothermal operations).