Bài 18:
a: =>1,2:x=4/3
=>x=9/10
b: =>\(4.5\cdot x=1.5:2.5=\dfrac{3}{5}\)
hay x=2/15
179.
\(a.\) \(20:12+7:12=\left(20+7\right):12=\dfrac{27}{12}=\dfrac{9}{4}.\)
\(b.\) \(259:15-136:15=\left(259-136\right):15=123:15=\dfrac{123}{15}=\dfrac{41}{5}.\)
180.
\(a.\) \(1,9:x+1,7:x=2,4.\Leftrightarrow\left(1,9+1,7\right):x=2,4.\Leftrightarrow3,6:x=2,4.\)
\(\Leftrightarrow x=1,5.\)
\(b.\) \(3:x-0,3:x=3,6.\Leftrightarrow\left(3-0,3\right):x=3,6.\Leftrightarrow2,7:x=3,6.\Leftrightarrow x=0,75.\)
\(c.\) \(x\times2,3+x:10=7,56.\Leftrightarrow x\times2,3+x\times\dfrac{1}{10}=7,56.\)
\(\Leftrightarrow x\times2,3+x\times0,1=7,56.\Leftrightarrow x\times\left(2,3+0,1\right)=7,56.\)
\(\Leftrightarrow x\times2,4=7,56.\Leftrightarrow x=3.15.\)
\(d.\) \(x\times3,05-x:100=7,6.\Leftrightarrow x\times3,05-x\times\dfrac{1}{100}=7,6.\)
\(\Leftrightarrow x\times3,05-x\times0,01=7,6.\Leftrightarrow x\times\left(3,05-0,01\right)=7,6.\)
\(\Leftrightarrow x\times3,04=7,6.\Leftrightarrow x=2,5.\)
\(e.\) \(x:0,25+x\times11=1,8.\Leftrightarrow x:\dfrac{1}{4}+x\times11=1,8.\)
\(\Leftrightarrow x\times4+x\times11=1,8.\Leftrightarrow x\times\left(4+11\right)=1,8.\)
\(\Leftrightarrow x\times15=1,8.\Leftrightarrow x=0,12.\)
