= Solution
At leading order the <Higgs decay to a fermion pair> has
$$
\Gamma_f=N_c^f\frac{m_f^2m_H}{8\pi v^2}
\left(1-\frac{4m_f^2}{m_H^2}\right)^{3/2}.
$$
Each <quark> contributes three distinguishable colour states, whereas a lepton has one. Neglecting the small phase-space factors for these masses, radiative corrections and the scale dependence of <quark> masses, the requested ratio is
$$
\boxed{\Gamma_\tau:\Gamma_c:\Gamma_b
=m_\tau^2:3m_c^2:3m_b^2
=3.24:6.75:75
=1:2.083:23.15.}
$$
The numerical masses here are those printed with question 3; the tau and <electron> approximations deliberately differ from those in question 1. Omitting the <quark> colour multiplicity would give the wrong relative rates.
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