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Bài 2:
a:
1: \(\dfrac{a}{b}=\dfrac{c}{d}\)
\(\Leftrightarrow\dfrac{a+b}{a}=\dfrac{c+d}{c}\)
hay \(\dfrac{a}{a+b}=\dfrac{c}{c+d}\)
a: \(2,5:4x=0,5:0,2\)
=>\(2,5:4x=0,5\cdot5=2,5\)
=>4x=1
=>\(x=\dfrac{1}{4}\)
b: \(3,8:2x=\dfrac{1}{4}:2\dfrac{2}{3}\)
=>\(3,8:2x=\dfrac{1}{4}:\dfrac{8}{3}=\dfrac{1}{4}\cdot\dfrac{3}{8}=\dfrac{3}{32}\)
=>\(2x=3,8:\dfrac{3}{32}=\dfrac{19}{5}\cdot\dfrac{32}{3}=\dfrac{608}{15}\)
=>\(x=\dfrac{608}{15}:2=\dfrac{304}{15}\)
c: \(5,25:7x=3,6:2,4\)
=>\(5,25:7x=1,5\)
=>\(7x=5,25:1,5=3,5\)
=>\(x=\dfrac{3.5}{7}=0,5\)
d: \(1,8:1,3=-2,7:5x\)
=>\(5x=-2,7:\dfrac{18}{13}=-2,7\cdot\dfrac{13}{18}=-1,95\)
=>\(x=-1,95:5=-0,39\)
a) \(2,5:2,7=x:\frac{3}{5}\)
\(\Rightarrow\frac{5}{2}:\frac{27}{10}=x.\frac{5}{3}\)
\(\Rightarrow\frac{5}{2}.\frac{10}{27}=\frac{5x}{3}\)
\(\Rightarrow\frac{25}{27}=\frac{5x}{3}\)
\(\Rightarrow5x=\frac{25.3}{27}=\frac{75}{27}=\frac{25}{9}\)
\(\Rightarrow x=\frac{25}{9}:5=\frac{25}{9}.\frac{1}{5}=\frac{5}{9}\)
b) \(\frac{19}{5}:\frac{608}{15}=0,25:x\)
\(\Rightarrow\frac{19}{5}.\frac{15}{608}=\frac{1}{4}:x\)
\(\Rightarrow\frac{3}{32}=\frac{1}{4}:x\)
\(\Rightarrow x=\frac{1}{4}:\frac{3}{32}=\frac{1}{4}.\frac{32}{3}=\frac{8}{3}\)
c/ \(\frac{8}{3}:x=\frac{16}{9}:0,2\)
\(\Rightarrow\frac{8}{3}:x=\frac{16}{9}:\frac{1}{5}=\frac{16}{9}.5=\frac{80}{9}\)
\(\Rightarrow x=\frac{8}{3}:\frac{80}{9}=\frac{8}{3}.\frac{9}{80}=\frac{3}{10}\)
a) \(1,25:0,8=\frac{3}{8}:0,2x\)
\(\Rightarrow\frac{3}{8}:0,2x=\frac{25}{16}\)
\(\Rightarrow0,2x=\frac{3}{8}:\frac{25}{16}=\frac{6}{25}\)
\(\Rightarrow x=\frac{6}{25}:\frac{1}{5}=\frac{6}{5}\)
b) \(1,8:1,3=\left(-2,7\right):5x\)
\(\Rightarrow\frac{-27}{10}:5x=\frac{18}{13}\)
\(\Rightarrow5x=\frac{-27}{10}:\frac{18}{13}=\frac{-39}{20}\)
\(\Rightarrow x=\frac{-39}{100}\)
a) \(\dfrac{x}{3}=\dfrac{-10}{6}\)
\(x\times6=-10\times3\)
\(x\times6=-30\)
\(x=-5\)
b) \(\dfrac{-8}{x}=\dfrac{-9}{15}\)
\(x\times-9=15\times-8\)
\(x\times-9=-120\)
\(x=\dfrac{40}{3}\)
c) \(\dfrac{2,7}{0,9}=\dfrac{-8}{x}\)
\(x\times2,7=-8\times0,9\)
\(x\times2,7=-7,2\)
\(x=-\dfrac{8}{3}\)
d) \(\dfrac{4}{9}=\dfrac{x}{12}\)
\(x\times9=12\times4\)
\(x\times9=48\)
\(x=\dfrac{48}{9}\)
\(x=\dfrac{16}{3}\)
a)
\(3\frac{4}{5}:40\frac{8}{15}=0,25:x\)
\(\Rightarrow\frac{19}{5}:\frac{608}{15}=\frac{1}{4}.x\)
\(\Rightarrow\frac{1}{4}.x=\frac{3}{32}\)
\(\Rightarrow x=\frac{3}{8}\)
Vậy x = 3 / 8
b) \(\frac{5}{6}:x=20:3\)
\(\Rightarrow\frac{5}{6x}=\frac{20}{3}\)
\(\Rightarrow120x=15\)
\(\Rightarrow x=\frac{1}{5}\)
Vậy x = 1 / 5
c)
\(x:2,5=0,003:0,75\)
\(\Rightarrow x.\frac{2}{5}=\frac{3}{1000}.\frac{4}{3}\)
\(\Rightarrow x.\frac{2}{5}=\frac{1}{250}\)
\(\Rightarrow x=\frac{1}{100}\)
d)
\(\frac{2}{3}:0,4=x:\frac{4}{5}\)
\(\Rightarrow\frac{2}{3}:\frac{2}{5}=\frac{5x}{4}\)
\(\Rightarrow\frac{5x}{4}=\frac{5}{3}\)
\(\Rightarrow15x=20\)
\(\Rightarrow x=\frac{4}{3}\)
Vậy x = 4 / 3
ii: Ta có: 15:4=x:3.5
nên \(x=\dfrac{3.5\cdot15}{4}=\dfrac{105}{8}\)