Question

Biết X + X x 1/4 : 2/7 + X : 2/9 = 255

1 1/21 : < 15,75 - 15 1/5 > + 2 1/12 : < 7 3/4 - 7,25 >

Answer 1

a) \(x+x\times\frac{1}{4}\div\frac{2}{7}+x\div\frac{2}{9}=255\)

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

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

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

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

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

\(\Rightarrow x=40\)

Vậy x = 40

b) \(1\frac{1}{21}\div\left(15,75-15\frac{1}{5}\right)+2\frac{1}{12}\div\left(7\frac{3}{4}-7,25\right)\)

\(=\frac{22}{21}\div\left(15,75-\frac{76}{5}\right)+\frac{25}{12}\div\left(\frac{31}{4}-7,25\right)\)

\(=\frac{22}{21}\div\frac{11}{20}+\frac{25}{12}\div\frac{1}{2}\)

\(=\frac{40}{21}+\frac{25}{6}\)

\(=\frac{85}{14}\)

_Chúc bạn học tốt_

Answer 2

X + X x 1/4 : 2/7 + x : 2/9 = 225

X + X x 1/4 x 7/2 + X x 9/2 = 225

X + X x 7/8 + X x 9/2 = 225

X x ( 1 + 7/8 + 9/2 ) = 225

X x 51/8 = 225

X = 225 : 51/8

X = 600/17