Thực hiện phép tính : a, (1/2+3/5-1/3)×0,8+0,5×(-2/1/2):1/1/4 b, 1-/4×13/9/11-0,25×6/2/11

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1. Đáp án:

   $\begin{array}{l}
   a)\left( {\dfrac{1}{2} + \dfrac{3}{5} – \dfrac{1}{3}} \right).0,8 + 0,5.\left( { – 2\dfrac{1}{2}} \right):1\dfrac{1}{4}\\
    = \dfrac{{15 + 3.6 – 10}}{{30}}.\dfrac{8}{{10}} + \dfrac{5}{{10}}.\left( { – \dfrac{5}{2}} \right):\dfrac{5}{4}\\
    = \dfrac{{23}}{{30}}.\dfrac{4}{5} + \dfrac{1}{2}.\left( { – \dfrac{5}{2}} \right).\dfrac{4}{5}\\
    = \dfrac{{46}}{{75}} – 1\\
    = \dfrac{{ – 29}}{{75}}\\
   b)\dfrac{1}{4}.13\dfrac{9}{{11}} – 0,25.6\dfrac{2}{{11}}\\
    = \dfrac{1}{4}.\dfrac{{152}}{{11}} – \dfrac{{25}}{{100}}.\dfrac{{68}}{{11}}\\
    = \dfrac{1}{4}.\dfrac{{152}}{{11}} – \dfrac{1}{4}.\dfrac{{68}}{{11}}\\
    = \dfrac{1}{4}.\left( {\dfrac{{152}}{{11}} – \dfrac{{68}}{{11}}} \right)\\
    = \dfrac{1}{4}.\dfrac{{84}}{{11}}\\
    = \dfrac{{21}}{{11}}
   \end{array}$

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