Câu 9:
5/56+1/8=5/56+7/56=12/56=3/14
\(\dfrac{17}{35}-\dfrac{2}{7}=\dfrac{17}{35}-\dfrac{10}{35}=\dfrac{7}{35}=\dfrac{1}{5}\)
\(\dfrac{7}{9}\cdot\dfrac{6}{5}=\dfrac{42}{45}=\dfrac{14}{15}\)
\(\dfrac{9}{7}:\dfrac{1}{4}=\dfrac{9}{7}\cdot4=\dfrac{36}{7}\)
Câu 10:
\(4m^238dm^2=438dm^2\)
6 phút 39 giây=339 giây
\(\dfrac{4}{5}m^2=80dm^2\)
3/4 thế kỷ=75 năm