Bài 1:tính A:(5/2+1/3):(1-2/3) B:(5/2-1/7)×9/2-6/7 C: 254 x 399145 ——————– 254 + 399 x 253 D: 5932 + 6001 x 5932 ———-

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1. Bài 1:

   A=($\frac{5}{2}$+$\frac{1}{3}$):(1-$\frac{2}{3}$)

     =($\frac{15}{6}$+$\frac{2}{6}$):($\frac{3}{3}$-$\frac{2}{3}$)

     =$\frac{15+2}{6}$÷$\frac{3-2}{3}$ 

     =$\frac{17}{6}$÷$\frac{1}{3}$

     =$\frac{17}{6}×3=$\frac{17×3}{6}$=$\frac{17}{2}$

   B=($\frac{5}{2}$-$\frac{1}{7}$)×$\frac{9}{2}$-$\frac{6}{7}$

     =($\frac{35}{14}$-$\frac{2}{14}$)×$\frac{9}{2}$-$\frac{6}{7}$

     =$\frac{35-2}{14}$×$\frac{9}{2}$-$\frac{6}{7}$

     =$\frac{33}{14}$×$\frac{9}{2}$-$\frac{6}{7}$

     =$\frac{33×9}{14×2}-$\frac{6}{7}$

     =$\frac{297}{28}$-$\frac{6}{7}$

     =$\frac{297}{28}$-$\frac{24}{28}$

     =$\frac{297-24}{28}$=$\frac{39}{4}$

   C=$\frac{254×399-145}{254+399×253}$ (mình có thay đổi đề bài chút)

     =$\frac{253×399+399-145}{254+399×253}$

     =$\frac{253×399+254}{254+399×253}$

     =1

   D=$\frac{5863+6001×5932}{5932×6002-69}$ (mình có thay đổi đề bài chút)

      =$\frac{5863+6001×5932}{5932×6001+5932-69}$ 

      =$\frac{5863+6001×5932}{5932×6001+5863}$

      =1

   Bài 2:

   B=(1-$\frac{1}{2}$)×(1-$\frac{1}{3}$)×(1-$\frac{1}{4}$)×…×(1-$\frac{1}{2019}$)×(1-$\frac{1}{2020}$) (mình thay đổi đề 1 chút nhé)

     =($\frac{2}{2}$-$\frac{1}{2}$)×($\frac{3}{3}$-$\frac{1}{3}$)×($\frac{4}{4}$-$\frac{1}{4}$)×…×($\frac{2019}{2019}$-$\frac{1}{2019}$)×($\frac{2020}{2020}$-$\frac{1}{2020}$)

     =$\frac{2-1}{2}$×$\frac{3-1}{3}$×…×$\frac{2020-1}{2020}$

     =$\frac{1}{2}$×$\frac{2}{3}$×….×$\frac{2019}{2020}$

     =$\frac{1×2×3×…×2019}{2×3×4×…×2020}$

     =$\frac{1}{2020}$

   E=$5\frac{9}{10}$:$\frac{3}{2}$-(2$\frac{1}{3}$×$4\frac{1}{2}$-2×$2\frac{1}{3}$):$\frac{7}{4}$

     =$\frac{59}{10}$×$\frac{2}{3}$-($\frac{7}{3}$×$\frac{9}{2}$-2×$\frac{7}{3}$)×$\frac{4}{7}$

     =$\frac{59×2}{10×3}$-($\frac{7×9}{3×2}$-$\frac{2×7}{3}$)×$\frac{4}{7}$

     =$\frac{59}{15}$-($\frac{21}{2}$-$\frac{14}{3}$)×$\frac{4}{7}$

     =$\frac{59}{15}$-($\frac{63}{6}$-$\frac{28}{6}$)×$\frac{4}{7}$

     =$\frac{59}{15}$-$\frac{63-28}{6}$×$\frac{4}{7}$

     =$\frac{59}{15}$-$\frac{35}{6}$×$\frac{4}{7}$

     =$\frac{59}{15}$-$\frac{35×4}{6×7}$

     =$\frac{59}{15}$-$\frac{10}{3}$

     =$\frac{59}{15}$-$\frac{50}{15}$

     =$\frac{59-50}{15}$=$\frac{9}{15}$=$\frac{3}{5}$

   Bài 3: 

   a) x+$2\frac{3}{4}$=$5\frac{2}{3}$

   ⇒ x+$\frac{11}{4}$=$\frac{17}{3}$

   ⇒ x=$\frac{17}{3}$- $\frac{11}{4}$

         =$\frac{68}{12}$-$\frac{33}{12}$

         =$\frac{68-33}{12}$=$\frac{35}{12}$

   b) x-1×$\frac{4}{5}$=$3\frac{2}{7}$

   ⇒ x-$\frac{4}{5}$=$\frac{23}{7}$

   ⇒ x=$\frac{23}{7}$+$\frac{4}{5}$

         =$\frac{115}{35}$+$\frac{28}{35}$

         =$\frac{115+28}{35}$=$\frac{143}{35}$

   c) x×$3\frac{1}{2}$=$4\frac{3}{4}$

   ⇒ x×$\frac{7}{2}$=$\frac{19}{4}$

   ⇒ x=$\frac{19}{4}$÷$\frac{7}{2}$

         =$\frac{19}{4}$×$\frac{2}{7}$

         =$\frac{19×2}{4×7}$

         =$\frac{19}{14}$

   d) x÷$2\frac{2}{3}$=$4\frac{1}{3}$

   ⇒ x÷$\frac{8}{3}$=$\frac{13}{3}$

   ⇒ x=$\frac{13}{3}$×$\frac{8}{3}$

         =$\frac{13×8}{3×3}$ 

         =$\frac{104}{9}$

   Trả lời

2. Bài 1:
   $a) \left ( \frac{5}{2}+\frac{1}{3} \right ):\left ( 1-\frac{2}{3} \right )\\=\frac{17}{6}:\frac{1}{3}\\=\frac{17}{6}.3=\frac{17}{2}\\b) \left ( \frac{5}{2}-\frac{1}{7} \right ).\frac{9}{2}-\frac{6}{7}\\=\frac{33}{14}.\frac{9}{2}-\frac{6}{7}\\=\frac{297}{28}-\frac{6}{7}=\frac{39}{4}\\c) 254 x 399145=101382830\\  254 + 399 x 253\\=254+100947=101201\\d) 5932 + 6001 x 5932\\=5932+35597932=35598464\\5932 x 6001 – 69\\=35597932-69=35597863$
   Bài 2:
   $B=\left ( 1-\frac{1}{2} \right ).\left ( 1-\frac{1}{3} \right ).\left ( 1-\frac{1}{5} \right ).\left ( 1-\frac{1}{2009} \right ).\left ( 1-\frac{1}{2020} \right )\\=\frac{1}{2}.\frac{2}{3}.\frac{4}{5}.\frac{2008}{2009}.\frac{2019}{2020}\\=\frac{1}{3}.\frac{8032}{10045}.\frac{2019}{2020}\\=\frac{8032}{30135}.\frac{2019}{2020}=\frac{16216608}{60872700}\\E=5\frac{9}{10}:\frac{3}{2}-\left ( 2\frac{1}{3}.4\frac{1}{2}.2\frac{1}{3} \right ):\frac{7}{4}\\=\frac{59}{5}.\frac{2}{3}-\left ( \frac{7}{3}.\frac{9}{2}.\frac{7}{3} \right ).\frac{4}{7}\\=\frac{59}{5}.\frac{1}{3}-\left ( 7.\frac{3}{2}.\frac{7}{3} \right ).\frac{4}{7}\\=\frac{59}{15}-\left ( 7.\frac{1}{2}.7 \right ).\frac{4}{7}\\=\frac{59}{15}-\frac{49}{2}.\frac{4}{7}\\=\frac{59}{15}-7.2=-\frac{151}{15}$
   Bài 3:
   $a) x+2\frac{3}{4}=5\frac{2}{3}\\\Leftrightarrow x+\frac{11}{4}=\frac{17}{3}\\\Leftrightarrow x=\frac{17}{3}-\frac{11}{4}=\frac{35}{12}\\b) x-1.\frac{4}{5}=3\frac{2}{7}\\\Leftrightarrow x-\frac{4}{5}=\frac{23}{7}\\\Leftrightarrow x=\frac{23}{7}+\frac{4}{5}=\frac{143}{35}\\c) x.3\frac{1}{2}=4\frac{3}{4}\\\Leftrightarrow x.\frac{7}{2}=\frac{19}{4}\\\Leftrightarrow x=\frac{19}{4}:\frac{7}{2}=\frac{19}{4}\\d) x:2\frac{2}{3}=4\frac{1}{3}\\\Leftrightarrow x:\frac{8}{3}=\frac{13}{3}\\\Leftrightarrow x.\frac{3}{8}=\frac{13}{3}\\\Leftrightarrow x=\frac{13}{3}:\frac{3}{8}=\frac{104}{9}$

    

   Trả lời