Answers ( )Đáp án: a) 2; b) 1 Giải thích các bước giải: a) $\frac{2}{9}$ +$\frac{1}{5}$+$\frac{7}{9}$+$\frac{4}{5}$ =($\frac{2}{9}$ +$\frac{7}{9}$)+($\frac{1}{5}$+$\frac{4}{5}$) =1+1=2 b) $\frac{1}{12}$ +$\frac{3}{16}$+$\frac{5}{12}$+$\frac{5}{16}$ =($\frac{1}{12}$ +$\frac{5}{12}$)+($\frac{3}{16}$+$\frac{5}{16}$) =$\frac{1}{2}$+$\frac{1}{2}$=1 a) 2/9+ 1/5 + 7/9 + 4/5 = (2/9+ 7/9) + (1/5 + 4/5) = 9/9 + 5/5 = 1 +1 =2 b) 1/12 + 3/16 + 5/12 + 5/16 = (1/12 + 5/12) + (3/16 + 5/16) = 6/12 + 8/16 = 1/2 + 1/2 = 2/2 =1
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