\(n = \frac{{16}}{{20}} = \frac{4}{5}\)
==>\(n = {n_1} - {n_2} = \frac{v}{4}\left( {\frac{1}{{{l_1}}} - \frac{1}{{{l_2}}}} \right)\)
==>\(\frac{4}{5} = \frac{v}{4}\left( {\frac{1}{1} - \frac{1}{{1.01}}} \right) = \frac{{0.01v}}{{4 \times 1.01}}\)
\(v = \frac{{16 \times 101}}{5} = 323.2\,m{s^{ - 1}}\)