a) \(\dfrac{5}{7}+x=\dfrac{8}{9}\)
\(x=\dfrac{8}{9}-\dfrac{5}{7}\)
\(x=\dfrac{11}{63}\)
b) \(\dfrac{7}{9}\div x=\dfrac{2}{3}\)
\(x=\dfrac{7}{9}\div\dfrac{2}{3}\)
\(x=\dfrac{7}{6}\)
c) \(x\div\dfrac{1}{7}+\dfrac{6}{7}=1\)
\(x\div\dfrac{1}{7}=1-\dfrac{6}{7}\)
\(x\div\dfrac{1}{7}=\dfrac{1}{7}\)
\(x=\dfrac{1}{7}\times\dfrac{1}{7}\)
\(x=\dfrac{1}{49}\)
Bài 6
a) \(\dfrac{9}{10}+\dfrac{7}{8}+\dfrac{21}{10}+\dfrac{11}{9}+\dfrac{25}{8}+\dfrac{7}{9}\)
\(=\left(\dfrac{9}{10}+\dfrac{21}{10}\right)+\left(\dfrac{7}{8}+\dfrac{25}{8}\right)+\left(\dfrac{11}{9}+\dfrac{7}{9}\right)\)
\(=3+4+2=9\)
b) \(\dfrac{5}{8}\times\dfrac{5}{3}+\dfrac{1}{3}\times\dfrac{5}{8}\)
\(=\dfrac{5}{8}\times\left(\dfrac{5}{3}+\dfrac{1}{3}\right)\)
\(=\dfrac{5}{8}\times2\)
\(=\dfrac{10}{8}=\dfrac{5}{4}\)
Câu 6:
a: \(=\left(\dfrac{9}{10}+\dfrac{21}{10}\right)+\left(\dfrac{7}{8}+\dfrac{25}{8}\right)+\left(\dfrac{11}{9}+\dfrac{7}{9}\right)=3+4+2=9\)
b: \(=\dfrac{5}{8}\left(\dfrac{5}{3}+\dfrac{1}{3}\right)=\dfrac{5}{8}\cdot2=\dfrac{5}{4}\)
