Bài 4:
a: \(\dfrac{x}{15}=\dfrac{2}{3}\)
=>\(x=15\cdot\dfrac{2}{3}=10\)
b: \(x+\dfrac{-8}{13}=\dfrac{-21}{13}\)
=>\(x-\dfrac{8}{13}=-\dfrac{21}{13}\)
=>\(x=-\dfrac{21}{13}+\dfrac{8}{13}=-\dfrac{13}{13}=-1\)
c: \(\dfrac{2}{3}x-\dfrac{1}{2}=\dfrac{1}{10}\)
=>\(\dfrac{2}{3}x=\dfrac{1}{10}+\dfrac{1}{2}=\dfrac{1}{10}+\dfrac{5}{10}=\dfrac{6}{10}=\dfrac{3}{5}\)
=>\(x=\dfrac{3}{5}:\dfrac{2}{3}=\dfrac{9}{10}\)
d: \(\dfrac{3}{4}+\dfrac{1}{4}:x=-3\)
=>\(\dfrac{1}{4}:x=-3-\dfrac{3}{4}=-\dfrac{15}{4}\)
=>\(x=\dfrac{1}{4}:\dfrac{-15}{4}=\dfrac{-1}{15}\)
e: \(\left(\dfrac{2}{3}-x\right)\left(x-\dfrac{1}{4}\right)=0\)
=>\(\left[{}\begin{matrix}\dfrac{2}{3}-x=0\\x-\dfrac{1}{4}=0\end{matrix}\right.\)
=>\(\left[{}\begin{matrix}x=\dfrac{2}{3}\\x=\dfrac{1}{4}\end{matrix}\right.\)
f: 0,51-x=-0,35
=>x=0,51-(-0,35)
=>x=0,51+0,35=0,86
Bài 3:
a: \(-\dfrac{1}{2}+\dfrac{5}{6}+\dfrac{1}{3}\)
\(=\dfrac{-3+5+2}{6}=\dfrac{4}{6}=\dfrac{2}{3}\)
b: \(\dfrac{-3}{8}+\dfrac{7}{4}-\dfrac{1}{12}\)
\(=\dfrac{-9}{24}+\dfrac{42}{24}-\dfrac{2}{24}=\dfrac{31}{24}\)
c: \(\dfrac{3}{5}:\left(\dfrac{1}{4}\cdot\dfrac{7}{5}\right)\)
\(=\dfrac{3}{5}:\dfrac{7}{20}\)
\(=\dfrac{3}{5}\cdot\dfrac{20}{7}=\dfrac{3\cdot4}{7}=\dfrac{12}{7}\)
d: \(\dfrac{10}{11}+\dfrac{4}{11}:4-\dfrac{1}{8}\)
\(=\dfrac{10}{11}+\dfrac{1}{11}-\dfrac{1}{8}\)
\(=1-\dfrac{1}{8}=\dfrac{7}{8}\)
e: \(\dfrac{-5}{7}+\dfrac{8}{11}+\left(-\dfrac{2}{7}\right)+\dfrac{1}{4}+\dfrac{3}{11}\)
\(=\left(-\dfrac{5}{7}-\dfrac{2}{7}\right)+\left(\dfrac{8}{11}+\dfrac{3}{11}\right)+\dfrac{1}{4}\)
\(=-1+1+\dfrac{1}{4}=\dfrac{1}{4}\)
f: \(\dfrac{2}{7}\cdot\dfrac{5}{13}+\dfrac{2}{7}\cdot\dfrac{6}{13}-\dfrac{2}{7}\cdot1\dfrac{11}{13}\)
\(=\dfrac{2}{7}\cdot\left(\dfrac{5}{13}+\dfrac{6}{13}-1-\dfrac{11}{13}\right)\)
\(=\dfrac{2}{7}\cdot\left(-1\right)=-\dfrac{2}{7}\)
g: \(15,3-21,5-3\cdot1,5\)
=15,3-21,5-4,5
=15,3-26
=-10,7
h: \(2\left(4^2-2\cdot4,1\right)+1.25:5\)
=2(16-8,2)+0,25
=15,6+0,25
=15,85
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