A membrane system treating air with 1 percent CFC-11 produces a residue with 0.1 percent CFC-11 and a permeate of 4.9 percent CFC-11 with a stage cut of 19 percent. R 0.05. 

(a) What is the selectivity? 

(b) If the permeate is sent to a smaller second unit operating at the same value of R, what permeate composition could be reached if the residue from the second unit contains 1 percent CFC-11?