Question

Tính bằng cách thuận tiện.

a) 250 x 8 x 125 x 40                      b) \(\dfrac{1}{4}+\dfrac{11}{10}+\dfrac{6}{8}+\dfrac{9}{10}\)

c) \(\dfrac{7}{8}\times4\times\dfrac{1}{4}\times\dfrac{8}{7}\)                          d) \(\dfrac{4}{9}\times\dfrac{1}{9}+\dfrac{4}{9}\times\dfrac{8}{9}\)

Answer 1

a) 250 x 8 x 125 x 40 = (250 x 40) x (8 x 125)

                       = 10 000 x 1 000

                      = 10 000 000

$b)\frac{1}{4} + \frac{{11}}{{10}} + \frac{6}{8} + \frac{9}{{10}} = \left( {\frac{1}{4} + \frac{6}{8}} \right) + \left( {\frac{{11}}{{10}} + \frac{9}{{10}}} \right) = \left( {\frac{2}{8} + \frac{6}{8}} \right) + 2 = 1 + 2 = 3$

$c)\frac{7}{8} \times 4 \times \frac{1}{4} \times \frac{8}{7} = \left( {\frac{7}{8} \times \frac{8}{7}} \right) \times \left( {4 \times \frac{1}{4}} \right) = 1 \times 1 = 1$                         

$d)\,\,\frac{4}{9} \times \frac{1}{9} + \frac{4}{9} \times \frac{8}{9} = \frac{4}{9} \times \left( {\frac{1}{9} + \frac{8}{9}} \right) = \frac{4}{9} \times 1 = \frac{4}{9}$