1tính 0,5+0,5.(-80).0.01-10% 75%-3 1/2+0,5:5/12 2tìm x x-1 1/2x=5% 75%x-2/5x=3/10 giúp mk vs mn mai mk nộp r nhanh lên ạ

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1. Đáp án:

   1 a)0
   b) $\dfrac{-31}{20}$
   2)
   a) $x=\dfrac{-1}{10}\\
   b)x=\dfrac{6}{7}$

   Giải thích các bước giải:

   1a)$0,5+0,5.(-80).0,01-10$%
   $=0,5+0,5.(-0,8)-0,1\\
   =0,5-0,4-0,1=0$
   b) $75$%-$3\dfrac{1}{2}+0,5:\dfrac{5}{12}$
   $=0,75-\dfrac{7}{2}+0,5.\dfrac{12}{5}\\
   =\dfrac{3}{4}-\dfrac{7}{2}+\dfrac{1}{2}.\dfrac{12}{5}\\
   =\dfrac{3}{4}-\dfrac{7}{2}+\dfrac{6}{5}\\
   =\dfrac{15}{20}-\dfrac{70}{20}+\dfrac{24}{20}\\
   =\dfrac{15-70+24}{20}=\dfrac{-31}{20}$
   2)
   a) $x-1\dfrac{1}{2}x=5$%
   $\Leftrightarrow x-\dfrac{3}{2}x=\dfrac{5}{100}\\
   \Leftrightarrow x-\dfrac{3}{2}=\dfrac{1}{20}\\
   \Leftrightarrow \dfrac{2}{2}x-\dfrac{3}{2}x=\dfrac{1}{20}\\
   \Leftrightarrow \dfrac{-1}{2}x=\dfrac{1}{20}\\ \Leftrightarrow x=(-2).\dfrac{1}{20}=\dfrac{-1}{10}\\$
   b)$75$%x-$\dfrac{2}{5}x=\dfrac{3}{10}$
   $\Leftrightarrow \dfrac{3}{4}x-\dfrac{2}{5}x=\dfrac{3}{10}\\
   \Leftrightarrow \left ( \dfrac{3}{4}-\dfrac{2}{5} \right )x=\dfrac{3}{10}\\
   \Leftrightarrow \left (\dfrac{15}{20}-\dfrac{8}{20}  \right )x=\dfrac{3}{10}\\
   \Leftrightarrow \dfrac{15-8}{20}x=\dfrac{3}{10}\\
   \Leftrightarrow \dfrac{7}{20}x=\dfrac{3}{10}\\
   \Leftrightarrow x=\dfrac{3}{10}.\dfrac{20}{7}=\dfrac{6}{7}$

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