Tính bằng cách thuận tiện nhất 5/4 x 8/9 +8/9x7/8-8/9

a) 54  ×  89  +  89  ×  78  −  89

=89×54+78−1

=89×108+78−88

=89×98

= 1

b) \[\frac{2}{3}\,\,:\,\,\frac{5}{6}\,\, - \,\,\frac{1}{6}\,\,:\,\,\frac{3}{2}\,\, - \,\,1\,\,:\,\,\frac{3}{2}\]

\[ = \frac{2}{3} \times \frac{6}{5} - \frac{1}{6} \times \frac{2}{3} - 1 \times \frac{2}{3}\]

\[ = \frac{2}{3} \times \left( {\frac{6}{5} - \frac{1}{6} - 1} \right)\]

\[ = \frac{2}{3} \times \left( {\frac{{36}}{{30}} - \frac{5}{{30}} - \frac{{30}}{{30}}} \right)\]

=23  × 130 =23×2×15=145