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:

   1)
   a) 0,5+0,5.(-80).0,01-10%
   $=\dfrac{1}{2}+\dfrac{1}{2}.(-80).\dfrac{1}{100}-\dfrac{10}{100}\\
   =\dfrac{1}{2}-40.\dfrac{1}{100}-\dfrac{1}{10}\\
   =\dfrac{1}{2}-\dfrac{2}{5}-\dfrac{1}{10}\\
   =\dfrac{5}{10}-\dfrac{4}{10}-\dfrac{1}{10}\\
   =\dfrac{5-4-1}{10}=0$
   b) 75%-$3\dfrac{1}{2}+0,5:\dfrac{5}{12}$
   $=\dfrac{75}{100}-\dfrac{7}{2}+\dfrac{1}{2}.\dfrac{12}{5}\\
   =\dfrac{3}{4}-\dfrac{7}{2}+\dfrac{6}{5}\\
   =\dfrac{15}{20}-\dfrac{70}{20}+\dfrac{24}{20}\\
   =\dfrac{15-70+24}{20}\\
   =\dfrac{-31}{20}$
   2)
   $a) x-1\dfrac{1}{2}x=5.\dfrac{1}{100}\\
   \Leftrightarrow x-\dfrac{3}{2}x=\dfrac{1}{20}\\
   \Leftrightarrow \dfrac{2}{2}x-\dfrac{3}{2}x=\dfrac{1}{20}\\
   \Leftrightarrow \dfrac{-1}{2}x=\dfrac{1}{20}\\
   \Leftrightarrow x=\dfrac{1}{20}.(-2)=\dfrac{-1}{10}\\
   b) 
   \dfrac{75}{100}x-\dfrac{2}{5}x=\dfrac{3}{10}\\
   \Leftrightarrow \dfrac{3}{4}x-\dfrac{2}{5}x=\dfrac{3}{10}\\
   \Leftrightarrow \dfrac{15}{20}x-\dfrac{8}{20}x=\dfrac{3}{10}\\
   \Leftrightarrow \dfrac{7}{20}x=\dfrac{3}{10}\\
   \Leftrightarrow x=\dfrac{3}{10}.\dfrac{20}{7}=\dfrac{6}{7}$

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