a) 1,26 : x + 2,34 : x =5
\(1,26\times\frac{1}{x}+2,34\times\frac{1}{x}=5\)
\(\frac{1}{x}\times\left(1,26+2,34\right)=5\)
\(\frac{1}{x}\times3,6=5\)
\(\frac{1}{x}=5:3,6\)
\(\frac{1}{x}=\frac{18}{25}\)
\(x=\frac{25}{18}\)
b) \(x\times3,1+x\times6,9=30,4\)
\(x\times\left(3,1+6,9\right)=30,4\)
\(x\times10=30,4\)
\(x=30,4:10\)
\(x=3,04\)
c) \(x:1,5+0,45=7,65\)
\(x:1,5=7,65-0,45\)
\(x:1,5=7,2\)
\(x=1,5\times7,2\)
\(x=11,1\)
Chúc bn học tốt !