Assume that the number of neutrinos with mass << M_Z is 3, 4, or 5 in turn, without changing anything else. Evaluate for each case the Z branching ratio into μ⁺μ^- and the ratio Γ_μμ/Γ_Z. Evaluate the ratio of the cross-sections at the peak for e⁺e^- into hadrons for N = 3, 4 and 5.