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Bài 2

a) x=5

b)x=1

diễn giải ra nhé

X x \(\dfrac{3}{4}\)+ X x\(\dfrac{1}{5}\)+ X x \(\dfrac{1}{20}\)+ X= 1000

\(\dfrac{2}{5}\times\dfrac{1}{7}+\dfrac{2}{7}\times\dfrac{2}{5}\)

\(=\dfrac{2}{5}\times\left(\dfrac{1}{7}+\dfrac{2}{7}\right)\)

\(=\dfrac{2}{5}\times\dfrac{3}{7}\)

\(=\dfrac{6}{35}\)

\(x+\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}\)

\(x+\dfrac{1}{6}=\dfrac{3}{4}\)

\(x=\dfrac{9}{12}-\dfrac{2}{12}\)

\(x=\dfrac{7}{12}\)

\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times...\times\left(1-\dfrac{1}{2020}\right)+x=\dfrac{1}{2}\)

\(\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times...\times\dfrac{2019}{2020}+x=\dfrac{1}{2}\)

\(\dfrac{1}{2020}+x=\dfrac{1}{2}\)

\(x=\dfrac{1}{2}-\dfrac{1}{2020}\)

\(x=\dfrac{1010}{2020}-\dfrac{1}{2020}\)

\(x=\dfrac{1009}{2020}\)

\(\dfrac{2}{5}\times\dfrac{1}{7}+\dfrac{2}{7}\times\dfrac{2}{5}\)

\(=\dfrac{2}{5}\times\left(\dfrac{1}{7}+\dfrac{2}{7}\right)\)

\(=\dfrac{2}{5}\times\dfrac{3}{7}\)

\(=\dfrac{6}{35}\)

\(x+\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}\)

\(\Rightarrow\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}-x\)

\(\Rightarrow\dfrac{3}{4}-x=\dfrac{1}{6}\)

\(\Rightarrow x=\dfrac{3}{4}-\dfrac{1}{6}=\dfrac{7}{12}\)

\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times...\times\left(1-\dfrac{1}{2020}\right)+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times...\times\dfrac{2019}{2020}+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1\times2\times3\times4\times...\times2019}{2\times3\times4\times5\times...\times2020}+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{2020}+x=\dfrac{1}{2}\)

\(\Rightarrow x=\dfrac{1}{2}-\dfrac{1}{2020}=\dfrac{1009}{2020}\)

11/15x = 3/5

=> x =  3/5 : 11/5 = 3/11

\(=>x=\dfrac{3}{5}:\left(\dfrac{2}{5}+\dfrac{1}{3}\right)=\dfrac{3}{5}:\dfrac{11}{15}=\dfrac{9}{11}\)

9/11

1 / 5 + x = 3 / 7 + 1 / 3

1 / 5 + x = 16 /21

x            = 16 / 21 - 1 / 5

x            = 59 / 105

x - 1 / 2 = 2 / 3 - 1 / 5

x - 1 / 2 = 7 / 15

         x  = 7 / 15 + 1 / 2

         x  = 29 / 30

3 / 5 * x = 2 / 7+ 1 / 4

3 / 5 * x = 15 / 28

          x = 15 / 28 : 3 / 5

          x = 25 / 28

7 / 8 : x = 1 / 6 * 2 / 3

7 / 8 : x = 1 / 9

          x = 7 / 8 : 1 / 9

          x = 63 / 8

Ta có : \(\left[x\cdot\frac{1}{2}+2\right]:\frac{3}{5}+4=9.\)

=>         \(\left[x\cdot\frac{1}{2}+2\right]:\frac{3}{5}=9-4.\)

=>          \(\left[x\cdot\frac{1}{2}+2\right]:\frac{3}{5}=5.\)

=>                       \(x\cdot\frac{1}{2}+2=5\cdot\frac{3}{5}.\)

=>                        \(x\cdot\frac{1}{2}+2=3.\)

=>                                 \(x\cdot\frac{1}{2}=3+2.\)

=>                                 \(x\cdot\frac{1}{2}=5.\)

=>                                         \(x=5:\frac{1}{2}.\)

=>                                         \(x=5\cdot2.\)

=>                                         \(x=10.\)

Vậy x = 10 .

a)\(\left[x\times\frac{1}{2}+2\right]:\frac{3}{5}+4=9\)                              b)\(x\times\frac{2}{3}-\frac{1}{5}=\frac{2}{5}+1\)

  \(\left[x\times\frac{1}{2}+2\right]:\frac{3}{5}=9-4\)                                \(x\times\frac{2}{3}-\frac{1}{5}=\frac{7}{5}\)

  \(\left[x\times\frac{1}{2}+2\right]:\frac{3}{5}=5\)                                        \(x\times\frac{2}{3}=\frac{7}{5}+\frac{1}{5}\)

   \(x\times\frac{1}{2}+2=5\times\frac{3}{5}\)                                       \(x\times\frac{2}{3}=\frac{8}{5}\)

   \(x\times\frac{1}{2}+2=3\)                                                 \(x=\frac{8}{5}:\frac{2}{3}\)

   \(x\times\frac{1}{2}=3-2\)                                                \(x=\frac{8}{5}\times\frac{3}{2}\)

  \(x\times\frac{1}{2}=1\)                                                         \(x=\frac{12}{5}\)

  \(x=1:\frac{1}{2}\)

  \(x=2\)