Bài 6
\(\dfrac{45}{60}=\dfrac{3}{4}\)
\(\dfrac{2}{3}-\dfrac{3}{8}=\dfrac{16}{24}-\dfrac{9}{24}=\dfrac{7}{24}\)
\(\dfrac{3}{5}\div\dfrac{4}{5}+\dfrac{1}{2}\times\dfrac{2}{3}=\dfrac{3}{4}+\dfrac{2}{6}=\dfrac{13}{12}\)
\(\dfrac{2}{5}+\dfrac{3}{7}+\dfrac{3}{5}+\dfrac{4}{7}=\left(\dfrac{2}{5}+\dfrac{3}{5}\right)+\left(\dfrac{3}{7}+\dfrac{4}{7}\right)=1+1=2\)
\(\dfrac{28}{36}=\dfrac{7}{9}\)
\(\dfrac{2}{3}\times\dfrac{9}{5}=\dfrac{18}{15}\)
\(\dfrac{5}{4}\times x=\dfrac{3}{8}+\dfrac{1}{4}\)
\(\dfrac{5}{4}\times x=\dfrac{5}{8}\)
\(x=\dfrac{5}{8}\div\dfrac{5}{4}\)
\(x=\dfrac{1}{2}\)
\(\dfrac{2}{3}\times\dfrac{4}{9}+\dfrac{2}{3}\times\dfrac{5}{9}=\dfrac{2}{3}\times\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{2}{3}\times1=\dfrac{2}{3}\)
Câu 7
\(\dfrac{3}{12}=\dfrac{1}{4}\)
Chọn B