[tex]a. \: \: \: \: \frac{1}{5} \times \frac{2}{3} = \frac{1 \times 2}{5 \times 3} = \frac{2}{15} \\ \\ b. \: \: \: \: ( - \frac{2}{3} ) {}^{3} = - \frac{2}{3} \times ( - \frac{2}{3} ) \times ( - \frac{2}{3} ) = \\ \\ = - \frac{2 \times 2 \times 2}{3 \times 3 \times 3} = - \frac{8}{27} [/tex]
