Tính bằng cách thuận tiện.

87 x 16 293 – 87 x 6 293                                        

$\frac{9}{{14}} \times \frac{3}{7} + \frac{3}{7} \times \frac{5}{{14}} - \frac{2}{7}$

87 x 16 293 – 87 x 6 293 = 87 x (16 293 – 6 293)

                                         = 87 x 10 000

                                         = 870 000                     

$\frac{9}{{14}} \times \frac{3}{7} + \frac{3}{7} \times \frac{5}{{14}} - \frac{2}{7} = \frac{3}{7} \times \left( {\frac{9}{{14}} + \frac{5}{{14}}} \right) - \frac{2}{7} = \frac{3}{7} \times 1 - \frac{2}{7} = \frac{1}{7}$