Tính bằng cách thuận tiện nhất:
a) \(\frac{7}{11}\) + \(\frac{3}{4}\) + \(\frac{4}{11}\) + \(\frac{1}{4}\) ;
b) \(\frac{72}{99}\) - \(\frac{28}{99}\) - \(\frac{14}{99}\) ;
c) 69,78 + 35,97 +30,22 ;
d) 83,45 - 30,98 - 42,47 ;
a) \(\frac{7}{11}\) + \(\frac{3}{4}\) + \(\frac{4}{11}\) + \(\frac{1}{4}\) = (\(\frac{7}{11}\) + \(\frac{4}{11}\)) + (\(\frac{3}{4}\) + \(\frac{1}{4}\) ) = \(\frac{11}{11}\) + \(\frac{4}{4}\) = 1 +1 =2.
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b) \(\frac{72}{99}\) - \(\frac{28}{99}\) - \(\frac{14}{99}\) = \(\frac{72}{99}\) - (\(\frac{28}{99}\) -\(\frac{14}{99}\) ) = \(\frac{72}{99}\) - \(\frac{42}{99}\) = \(\frac{30}{99}\) = \(\frac{10}{33}\)
c) 69,78 + 35,97 +30,22 = (69,78 + 30,22) + 35.97
= 100 + 35,97 = 135,97.
d) 83,45 - 30,98 - 42,47 = 83,45 - (30,98 + 42,47)
= 83,45 - 73,45 = 10.