$$rac{3}{8}n + rac{5}{8}n + rac{1}{3}n = (rac{3}{8} + rac{5}{8} + rac{1}{3})n = (rac{9}{24} + rac{15}{24} + rac{8}{24})n = rac{32}{24}n = rac{4}{3}n = 1rac{1}{3}n$$