Câu hỏi của Đặng Hoài An

Question

Bài 1: Tìm x, biết:

a,  $\left(x+\dfrac{1}{4}-\dfrac{1}{3}\right):\left(2+\dfrac{1}{6}-\dfrac{1}{4}\right)=\dfrac{7}{46}$

b,  \(\dfrac{13}{15}-\left(\dfrac{13}{21}+x\right).\dfrac{7}{12}=\dfrac{7}...

ChaosKiz · Accepted Answer

Bài 1:

$a,\left(x+\dfrac{1}{4}-\dfrac{1}{3}\right):\left(2-\dfrac{1}{6}-\dfrac{1}{4}\right)=\dfrac{7}{46}$

$\left(x+\dfrac{1}{4}-\dfrac{1}{3}\right):\left(\dfrac{24+2-3}{12}\right)=\dfrac{7}{46}$

$\left(x+\dfrac{1}{4}-\dfrac{1}{3}\right):\dfrac{23}{12}=\dfrac{7}{46}$

$x+\dfrac{1}{4}-\dfrac{1}{3}=\dfrac{7}{46}.\dfrac{23}{12}$

$x+\dfrac{1}{4}-\dfrac{1}{3}=\dfrac{7}{24}$

$x+\dfrac{1}{4}=\dfrac{7}{24}+\dfrac{1}{3}$

$x+\dfrac{1}{4}=\dfrac{5}{8}$

$x=\dfrac{5}{8}-\dfrac{1}{4}=\dfrac{3}{8}$

Vậy $x=\dfrac{3}{8}$

$b,\dfrac{13}{15}-\left(\dfrac{13}{21}+x\right).\dfrac{7}{12}=\dfrac{7}{10}$

$\left(\dfrac{13}{21}+x\right).\dfrac{7}{12}=\dfrac{13}{15}-\dfrac{7}{10}$

$\left(\dfrac{13}{21}+x\right).\dfrac{7}{12}=\dfrac{1}{6}$

$\dfrac{13}{21}+x=\dfrac{1}{6}:\dfrac{7}{12}$

$\dfrac{13}{21}+x=\dfrac{2}{7}$

$x=\dfrac{2}{7}-\dfrac{13}{21}=-\dfrac{1}{3}$

Vậy $x=-\dfrac{1}{3}$

Bài 2:

$a,\left(2\dfrac{5}{6}+1\dfrac{4}{9}\right):\left(10\dfrac{1}{12}-9\dfrac{1}{2}\right)$

$=\left(\dfrac{17}{6}+\dfrac{13}{9}\right):\left(\dfrac{121}{12}-\dfrac{19}{2}\right)$

$=\dfrac{77}{18}:\dfrac{7}{12}$

$=\dfrac{22}{3}$

$b,1\dfrac{5}{18}-\dfrac{5}{18}.\left(\dfrac{1}{15}+1\dfrac{1}{12}\right)$

$=\dfrac{23}{18}-\dfrac{5}{18}.\dfrac{69}{60}$

$=\dfrac{23}{18}-\dfrac{23}{72}$

$=\dfrac{23}{24}$

$c,-\dfrac{1}{7}.\left(9\dfrac{1}{2}-8,75\right):\dfrac{2}{7}+0,625:1\dfrac{2}{3}$

$=\dfrac{-1}{7}.\dfrac{3}{4}:\dfrac{2}{7}+\dfrac{5}{8}:\dfrac{5}{3}$

$=-\dfrac{3}{8}+\dfrac{5}{8}:\dfrac{5}{3}$

$=-\dfrac{3}{8}+\dfrac{3}{8}$

$=\dfrac{0}{8}=0$

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