tính bằng cách thuận tiện nhất
2/5 x 3/4 x 5/6 : 3/4
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\(\frac{2}{3}\times\frac{3}{4}\times\frac{4}{5}\times\frac{5}{6}\)
\(=\frac{2\times3\times4\times5}{3\times4\times5\times6}\)
\(=\frac{2}{6}\)
\(=\frac{1}{3}\)
5,5 + \(\dfrac{3}{4}\) - 5 + \(\dfrac{1}{4}\)
(5,5 - 5) + (\(\dfrac{3}{4}\) + \(\dfrac{1}{4}\))
= 0,5 + 1
= 1,5
\(\dfrac{5}{2}\) x \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) : \(\dfrac{3}{2}\)
= \(\dfrac{5}{2}\) x \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) x \(\dfrac{2}{3}\)
= (\(\dfrac{5}{2}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)
= (\(\dfrac{10}{4}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)
= \(\dfrac{11}{4}\) x \(\dfrac{2}{3}\)
= \(\dfrac{11}{6}\)
Tính \(x\):
435 - [\(x\) + 16] = 425 : 17
435 - [\(x\) + 16] = 25
[\(x\) + 16] = 435 - 25
\(x\) + 16 = 410
\(x\) = 410 - 16
\(x\) = 394
\(\Rightarrow x\times\left(\dfrac{9}{5}+\dfrac{6}{5}\right)=\dfrac{3}{4}\\ \Rightarrow x\times3=\dfrac{3}{4}\\ \Rightarrow x=\dfrac{3}{4}:3\\ \Rightarrow x=\dfrac{3}{4}\times\dfrac{1}{3}=\dfrac{1}{4}\)
\(\dfrac{9}{5}\times x+\dfrac{6}{5}\times x=\dfrac{3}{4}\)
\(x\times\left(\dfrac{9}{5}+\dfrac{6}{5}\right)=\dfrac{3}{4}\)
\(x\times3=\dfrac{3}{4}\)
\(x=\dfrac{3}{4}:3=\dfrac{3}{4}\times\dfrac{1}{3}\)
\(x=4\)
\(5\dfrac{3}{4}:3+2\dfrac{1}{4}\times\dfrac{1}{3}-\dfrac{1}{8}=\left(5\dfrac{3}{4}+2\dfrac{1}{4}\right)\times\dfrac{1}{3}-\dfrac{1}{8}\\ =8\times\dfrac{1}{3}-\dfrac{1}{8}=\dfrac{8}{3}-\dfrac{1}{8}=\dfrac{61}{24}\\ ----\\ \dfrac{3}{5}:\dfrac{5}{6}:\dfrac{6}{7}:\dfrac{7}{8}+\dfrac{2}{5}+\dfrac{23}{35}\\ =\dfrac{3}{5}\times\dfrac{6}{5}\times\dfrac{7}{6}\times\dfrac{8}{7}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{18}{25}\times\dfrac{4}{3}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{353}{175}\)
= (2/5 x 5/6) x (3/4 : 3/4)
= 2/6 x 1
= 2/6
= 1/3
thank you Tú Cường Trần