Thực hiện phép tính một cách hợp lí: c) 11/12 ⋅ 7/15 + 11/12 ⋅ 8/15 − 23/12 .

c) \[\frac{{11}}{{12}} \cdot \frac{7}{{15}} + \frac{{11}}{{12}} \cdot \frac{8}{{15}} - \frac{{23}}{{12}}\]

\( = \frac{{11}}{{12}} \cdot \left( {\frac{7}{{15}} + \frac{8}{{15}}} \right) - \frac{{23}}{{12}}\)

\( = \frac{{11}}{{12}} \cdot \frac{{15}}{{15}} - \frac{{23}}{{12}}\)

\( = \frac{{11}}{{12}} - \frac{{23}}{{12}}\)

\( = \frac{{ - 12}}{{12}} = - 1.\)