Tính bằng cách thuận tiện nhất:
a] [689 + 875] + 125 ;
581 + [878 + 419].
b] [\[\frac{2}{7}\]+\[\frac{4}{9}\]] +\[\frac{5}{7}\];
\[\frac{17}{11}\]+ [\[\frac{7}{15}\]+\[\frac{5}{11}\]] ;
c] 5,87 + 28,69 + 4,13 ;
83,75 + 46,98 + 6,25 ;
a] [689 + 875] + 125 = 689 + [875 + 125] = 689 + 1000 = 1689.
581 + [878 + 419] = [581 + 419] = 878 = 1000 + 878 = 1878.
b][\[\frac{2}{7}\]+\[\frac{4}{9}\]] +\[\frac{5}{7}\]= [\[\frac{2}{7}\]+\[\frac{5}{7}\]] +\[\frac{4}{9}\] = 1 +\[\frac{4}{9}\] =\[1\frac{4}{9}\].
\[\frac{17}{11}\]+ [\[\frac{7}{15}\]+\[\frac{5}{11}\]] = [\[\frac{17}{11}\] +\[\frac{5}{11}\]] +\[\frac{7}{15}\]=\[\frac{22}{11}\]+\[\frac{7}{15}\] = 2 +\[\frac{7}{15}\] =\[2\frac{7}{15}\].
c]5,87 + 28,69 + 4,13 = [5,87 + 4,13] + 28,69 = 10 + 28,69 = 38,69.
83,75 + 46,98 + 6,25 = [83,75 + 6,25] + 46,98 = 90 + 46,98 = 136,98.