$-\frac{9}{16}a * 5\frac{1}{3}b$, если $a = -\frac{1}{2}, b = \frac{1}{12}$
$-\frac{9}{16}a * 5\frac{1}{3}b = (-\frac{9}{16} * 5\frac{1}{3})ab = (-\frac{9}{16} * \frac{16}{3})ab = (-\frac{3}{1} * \frac{1}{1})ab = -3ab$
если $a = -\frac{1}{2}, b = \frac{1}{12}$:
$-3 * (-\frac{1}{2}) * \frac{1}{12} = -1 * (-\frac{1}{2}) * \frac{1}{4} = \frac{1}{8}$

$-\frac{1}{7}m * 2,8n * (-1\frac{1}{12}p)$, если $m = 2\frac{1}{13}, n = -\frac{5}{9}, p = 20$
$-\frac{1}{7}m * 2,8n * (-1\frac{1}{12}p) = -\frac{1}{7}m * \frac{28}{10}n * (-\frac{13}{12}p) = -\frac{1}{7}m * \frac{14}{5}n * (-\frac{13}{12}p) = -\frac{1}{1}m * \frac{2}{5}n * (-\frac{13}{12}p) = \frac{26}{60}mnp = \frac{13}{30}mnp$
если $m = 2\frac{1}{13}, n = -\frac{5}{9}, p = 20$:
$\frac{13}{30}mnp = \frac{13}{30} * 2\frac{1}{13} * (-\frac{5}{9}) * 20 = \frac{13}{30} * \frac{27}{13} * (-\frac{5}{9}) * 20 = \frac{1}{1} * \frac{1}{1} * (-\frac{1}{1}) * 10 = -10$