The correct option is (a) E = \(\frac{t^{N-1}}{τ^N}\frac{N^N}{(N-1)!}e^\frac{-tN}{τ}\)
The best explanation: For N tanks in series, the exit age distribution is, E = \(\frac{t^{N-1}}{τ^N}\frac{N^N}{(N-1)!}e^\frac{-tN}{τ}.\) The number of tanks in series, N = \(\frac{τ^2}{σ^2}. \)