Thực hiện phép tính:

a) \[\frac{1}{5} + \frac{4}{5}.\frac{{ - 3}}{8}\];

 \[ = \frac{1}{5} + \frac{{ - 3}}{{10}}\]

 \( = \frac{2}{{10}} + \frac{{ - 3}}{{10}}\)

 \( = \frac{{ - 1}}{{10}}\).

b)\(\frac{6}{7} \cdot \frac{2}{{13}} + \frac{{ - 15}}{{13}} \cdot \frac{6}{7}\);

 \( = \frac{6}{7} \cdot \left( {\frac{2}{{13}} + \frac{{ - 15}}{{13}}} \right)\)

 \( = \frac{6}{7} \cdot ( - 1)\)

 \( = \frac{{ - 6}}{7}\).

c) \[\frac{{{{25}^{25}}{{.7}^{30}}}}{{{5^{48}}{{.49}^{16}}}}\].

 \[ = \frac{{{{\left( {{5^2}} \right)}^{25}}{{.7}^{30}}}}{{{5^{48}}.{{\left( {{7^2}} \right)}^{16}}}} = \frac{{{5^{50}}{{.7}^{30}}}}{{{5^{48}}{{.7}^{32}}}}\]

 \[ = \frac{{{5^2}.1}}{{{{1.7}^2}}}\]

 \( = \frac{{25}}{{49}}\).