Thực hiện phép tính: (a) 7/23.[(-8/6) - 45/18]

a) \(\frac{7}{{23}}.\left[ {\left( { - \frac{8}{6}} \right) - \frac{{45}}{{18}}} \right]\)

\( = \frac{7}{{23}}\left[ {\left( { - \frac{{24}}{{18}}} \right) - \frac{{45}}{{18}}} \right]\)

\( = \frac{7}{{23}}.\frac{{ - 24 - 45}}{{18}} = \frac{7}{{23}}.\frac{{ - 69}}{{18}}\)

\( = \frac{7}{{23}}.\frac{{ - 3.23}}{{3.6}}\)\( = \frac{{ - 7}}{6}\).

b) \(16\frac{2}{7}:\left( { - \frac{3}{5}} \right) + 28\frac{2}{7}:\frac{3}{5}\)

\( = 16\frac{2}{7}.\frac{{ - 5}}{3} + 28\frac{2}{7}.\frac{5}{3}\)

\( = \frac{5}{3}\left( { - 16\frac{2}{7} + 28\frac{2}{7}} \right)\)

\( = \frac{5}{3}\left( { - 16 - \frac{2}{7} + 28 + \frac{2}{7}} \right)\)

\( = \frac{5}{3}.12 = 20\).