Question

Giúp câu 7,8

Answer 1

Câu 7:

a: \(18+\dfrac{9}{3}=18+3=21\)

b: \(\dfrac{4}{9}-\dfrac{5}{18}=\dfrac{8}{18}-\dfrac{5}{18}=\dfrac{3}{18}=\dfrac{1}{6}\)

c: \(\dfrac{3}{5}:\dfrac{5}{7}=\dfrac{3}{5}\cdot\dfrac{7}{5}=\dfrac{21}{25}\)

d: \(\dfrac{4}{7}\cdot\dfrac{2}{7}=\dfrac{4\cdot2}{7\cdot7}=\dfrac{8}{49}\)

Câu 8:

a: \(\dfrac{5}{4}\cdot x=\dfrac{3}{8}+\dfrac{5}{12}\)

=>\(x\cdot\dfrac{5}{4}=\dfrac{9+10}{24}=\dfrac{19}{24}\)

=>\(x=\dfrac{19}{24}:\dfrac{5}{4}=\dfrac{19}{24}\cdot\dfrac{4}{5}=\dfrac{19}{6\cdot5}=\dfrac{19}{30}\)

b: \(3\cdot\dfrac{7}{10}+\dfrac{7}{10}\cdot5+2\cdot\dfrac{7}{10}\)

\(=\dfrac{7}{10}\left(3+5+2\right)\)

\(=\dfrac{7}{10}\cdot10=7\)