$\frac{1}{3} * \frac{3}{4} = \frac{3}{12} = \frac{1}{4}$;
$\frac{1}{4} * \frac{4}{5} = \frac{4}{20} = \frac{1}{5}$;
$\frac{1}{5} * \frac{5}{6} = \frac{1}{6}$;
$\frac{1}{6} * \frac{6}{7} = \frac{1}{7}$.

$\frac{5}{12} * 6 = \frac{5}{2} = 2\frac{1}{2}$;
$\frac{5}{12} * 3 = \frac{5}{4} = 1\frac{1}{4}$;
$\frac{5}{12} * 4 = \frac{5}{3} = 1\frac{2}{3}$;
$\frac{5}{12} * 0 = 0$.