7 : 4 hay \(\dfrac{7}{4}\)

6 : 2 hay \(\dfrac{6}{2}\) hay \(\dfrac{3}{1}\)

4 : 10 hay \(\dfrac{4}{10}\) hay \(\dfrac{2}{5}\)

1. B 

2. B

3. A

Giải thích: \(\dfrac{2}{3}=\dfrac{8}{12};\dfrac{1}{4}=\dfrac{3}{12}\)

4. D

Giải thích: \(\dfrac{4}{5}=\dfrac{4\times7}{5\times7}=\dfrac{28}{35};\dfrac{3}{7}=\dfrac{3\times5}{7\times5}=\dfrac{15}{35}\)

Would

\(x=289\)

A

VD: Tỉ số của 3 và 5 = \(3\div5=\dfrac{3}{5}\)

A

\(a)\) \(x-\dfrac{1}{4}=\dfrac{3}{5}\)

\(x=\dfrac{3}{5}+\dfrac{1}{4}=\dfrac{12+5}{20}\)

\(x=\dfrac{17}{20}\)

\(b)\)\(x\div\dfrac{2}{3}=\dfrac{1}{2}\)

   \(x=\dfrac{1}{2}\times\dfrac{2}{3}\)

   \(x=\dfrac{1}{3}\)

A