Question

12+x/42=5/6 

25-x/40=3/8

Answer 1

\(a,12+\frac{x}{42}=\frac{5}{6}\)

\(\Rightarrow\frac{x}{42}=\frac{5}{6}-12\)

\(\Rightarrow\frac{x}{42}=\frac{-67}{6}\)

\(\Leftrightarrow6x=42\times(-67)\)

\(\Leftrightarrow6x=-2814\)

\(\Leftrightarrow x=-2814\div6=-469\)

Vậy x = -469

\(b,25-\frac{x}{40}=\frac{3}{8}\)

\(\frac{x}{40}=25-\frac{3}{8}\)

\(\frac{x}{40}=\frac{197}{8}\)

\(\Leftrightarrow8x=40\times197\)

\(\Leftrightarrow8x=7880\)

\(\Leftrightarrow x=7880\div8=985\)

Vậy x = 985

Chúc bạn học tốt

Answer 2

a, \(12+\frac{x}{42}=\frac{5}{6}\Leftrightarrow\frac{x}{42}=-\frac{67}{6}\Leftrightarrow\frac{x}{42}=\frac{-469}{42}\)

Khử mẫu đi ta đc : \(x=-469\)

b, \(25-\frac{x}{40}=\frac{3}{8}\Leftrightarrow\frac{x}{40}=\frac{197}{8}\Leftrightarrow\frac{x}{40}=\frac{985}{40}\)

Khử mẫu đi ta đc : \(x=985\)

Answer 3

x/42=5/6-12

x/42=-67/6

x.6=42.-67

x.6=-2814

x=-2814:6

x=-469

Answer 4

x/40=25-3/8

x/40=197/8

x.8=40.197

x.8=7880

x=7880:8

x=985

Answer 5

cách khác

\(12+\frac{x}{42}=\frac{5}{6}\)

\(\Leftrightarrow\frac{504}{42}+\frac{x}{42}=\frac{5}{6}\)

\(\Leftrightarrow\frac{504+x}{42}=\frac{5}{6}\)

\(\Leftrightarrow\frac{504+x}{42}=\frac{35}{42}\)

khử mẫu ta có 

\(\Leftrightarrow504+x=35\)

\(\Leftrightarrow x=35-504=-469\)

\(25-\frac{x}{40}=\frac{3}{8}\)

\(\Leftrightarrow\frac{1000}{40}-\frac{x}{40}=\frac{3}{8}\)

\(\Leftrightarrow\frac{1000-x}{40}=\frac{3}{8}\)

\(\Leftrightarrow\frac{1000-x}{40}=\frac{15}{40}\)

khử mẫu ta có

\(\Leftrightarrow1000-x=15\)

\(\Leftrightarrow x=1000-15=985\)