Question

\(\text{Tìm }x\)

\(\text{a) }\frac{7}{x}=\frac{3}{12}\)                            \(\text{ b) }x+x\times\frac{1}{4}:\frac{2}{7}+x:\frac{2}{9}=255\)

\(\text{GIÚP MIK NHÉ !}\)

 

Answer 1

a) ( nhân chéo nha bạn )

\(\frac{7}{x}=\frac{3}{12}=\frac{1}{4}\)

=> x = 7 . 4

=> x = 28

Answer 2

b)

\(x+x\cdot\frac{1}{4}:\frac{2}{7}+x:\frac{2}{9}=255\)

\(x+x\cdot\frac{7}{8}+x\cdot\frac{9}{2}=255\)

\(x\cdot\left(1+\frac{7}{8}+\frac{9}{2}\right)=255\)

\(x\cdot\frac{51}{8}=255\)

\(x=40\)

Answer 3

a) \(\frac{7}{x}=\frac{3}{12}\)

\(\Rightarrow7.12=x.3\)

\(\Rightarrow81=x.3\)

\(\Rightarrow x=81:3\)

\(\Rightarrow x=27\)

b) \(x+x.\frac{1}{4}:\frac{2}{7}+x:\frac{2}{9}=255\)

   \(x+x.\frac{1}{4}.\frac{2}{7}+x.\frac{9}{2}=255\)

  \(x+x.\frac{1}{14}+x.\frac{9}{2}=255\)

\(x.\left(1+\frac{1}{14}+\frac{9}{2}\right)=255\)

\(x.\frac{39}{7}=255\)

\(x=255:\frac{39}{7}\)

\(x=\frac{595}{13}\)

Answer 4

b) \(x+x.\frac{1}{4}:\frac{2}{7}+x:\frac{2}{9}=255\)

\(\Rightarrow x+x.\frac{1}{4}.\frac{7}{2}+x.\frac{9}{2}=255\)

\(\Rightarrow x+x.\frac{7}{8}+x.\frac{9}{2}=255\)

\(\Rightarrow x\left(1+\frac{7}{8}+\frac{9}{2}\right)=255\)

\(\Rightarrow x.\frac{51}{8}=255\)

\(\Rightarrow x=255:\frac{51}{8}\)

\(\Rightarrow x=40\)