Question

Tính bằng cách thuận tiện.

a) \(\dfrac{5}{7}+\dfrac{8}{11}+\dfrac{2}{7}\)                     b) \(\dfrac{2}{7}\times\dfrac{4}{9}+\dfrac{2}{7}\times\dfrac{5}{9}\)

Answer 1

a) $\frac{5}{7} + \frac{8}{{11}} + \frac{2}{7} = \left( {\frac{5}{7} + \frac{2}{7}} \right) + \frac{8}{{11}} = 1 + \frac{8}{{11}} = \frac{{11}}{{11}} + \frac{8}{{11}} = \frac{{19}}{{11}}$

b) $\frac{2}{7} \times \frac{4}{9} + \frac{2}{7} \times \frac{5}{9} = \frac{2}{7} \times \left( {\frac{4}{9} + \frac{5}{9}} \right) = \frac{2}{7} \times 1 = \frac{2}{7}$