a ) \(x+x\times\frac{1}{3}\div\frac{2}{9}+x\div\frac{2}{7}=252\)

\(x\times1+x\times\frac{1}{3}\div\frac{2}{9}+x\div\frac{2}{7}=252\)

\(x\times1+x\times\frac{1}{3}\times\frac{9}{2}+x\times\frac{7}{2}=252\)

\(x\times1+x\times\frac{9}{6}+x\times\frac{7}{2}=252\)

\(x\times\left(1+\frac{9}{6}+\frac{7}{2}\right)=252\)

\(x\times6=252\)

\(x=252\div6\)

\(x=42\)

b ) \(\left(3\times x-0,8\right)\div x+14,5=15\)

\(\left(3\times x-0,8\right)\div x=15-14,5\)

\(\left(3\times x-0,8\right)\div x=0,5\)

\(0,8\div x=3-0,5\)

\(0,8\div x=2,5\)

\(x=0,8\div2,5\)

\(x=0,32\)

(X x 3 - 0,8) : X + 14,5 = 15

3*x-0/x-70=15

3*x-0=85

3*x=85

x=85/3

( 3 x - 0.8 ) : x + 14.5 = 15

( 3 x - 0.8 ) x \(\frac{1}{x}\)+ 14,5 = 15

3X x \(\frac{1}{x}\)- 0,8 x \(\frac{1}{x}\)= 0,5

\(\frac{3x}{x}-\frac{0,8}{x}=\frac{0,5x}{x}\)

=> 3x - 0,8 = 0,5x

     3x - 0,5x = 0,8

       2,5x = 0,8

            x = 2,5 : 0,8

            x = \(\frac{25}{8}=3,125\)

\(A=\left[0,8\cdot7+(0,8)^2\right]\cdot\left[1,25\cdot7-\frac{4}{5}\cdot1,25\right]-47,86\)

\(=0,8\cdot(7+0,8)\cdot1,25\cdot(7-0,8)-47,86\)

\(=0,8\cdot7,8\cdot1,25\cdot6,2-47,86\)

\(=48,36-47,86=0,5\)

\(B=\frac{(1,09-0,29)\cdot\frac{5}{4}}{(18,9-16,65)\cdot\frac{8}{9}}=\frac{0,8\cdot1,25}{2,25\cdot\frac{8}{9}}=\frac{1}{2}\)

\(A:B=0,5:\frac{1}{2}=\frac{1}{2}:\frac{1}{2}=\frac{1}{2}\cdot2=1\)

A gấp 1 lần B

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\(x=0,2\)