[tex]{2}^{ - 3} + ( \frac{1}{2} ) {}^{ - 3} = \frac{1}{2 {}^{3} } + 2 {}^{3} = \frac{1}{8} + 8 = 8 \frac{1}{8} = 8.125 \\ 25 {}^{ - 4} \div 5 {}^{ - 7} = (5 {}^{2} ) {}^{ - 4} \div 5 {}^{ - 7} = 5 {}^{ - 8} \div 5 {}^{ - 7} = 5 {}^{ - 8 - ( - 7)} = 5 {}^{ - 8 + 7} = 5 {}^{ - 1} = \frac{1}{5} = 0.2 \\ ( - 3) {}^{ - 3} \times ( \frac{1}{3} ) {}^{ - 3} = - \frac{1}{3 {}^{3} } \times 3 {}^{3} = - 1 [/tex]