Tính bằng cách thuận tiện. a) 65 780 × 48 + 52 × 65 780

a) 65 780 × 48 + 52 × 65 780

= 65 780 × (48 + 52)

= 65 780 × 100

= 6 578 000

b) \(\frac{2}{7}\,\, + \,\,\frac{1}{9}\,\, + \,\,\frac{{12}}{7}\,\, + \,\,\frac{{26}}{9}\)

\( = \left( {\frac{2}{7}\,\, + \,\frac{{12}}{7}} \right) + \,\left( {\frac{1}{9}\, + \,\frac{{26}}{9}} \right)\)

\( = \frac{{14}}{7} + \frac{{27}}{9}\,\)

= 2 + 3

= 5