16. According to Eq. 42-6, 1 1 1 P (EF +"E) = = = F e(E +"E-EF)/kT +1 e"E/kT +1 ex +1 where x ="E/kT . Also, 1 1 1 P (EF - "E) = = = . F-"E-EF)/kT e(E +1 e-"E/kT +1 e-x +1 Thus, 1 1 ex +1+e-x +1 P (EF +"E) +P (EF - "E) = + = =1 . ex +1 e-x +1 (e-x +1)(ex +1) A special case of this general result can be found in problem 13, where "E = 63 meV a nd P (EF + 63 meV) + P (EF - 63 meV) = 0.090 + 0.91 = 1.0.