\(x\times3,5-x\times2=30\)
\(x\times\left(3,5-2\right)=30\)
\(x\times1,5=30\)
\(x=30:1,5\)
\(x=20\)

\(\dfrac{3}{8}+\dfrac{9}{4}\)
\(=\dfrac{3}{8}+\dfrac{18}{8}\)
\(=\dfrac{21}{8}\)

\(\dfrac{5}{8}\times4+\dfrac{5}{8}\times\dfrac{4}{5}\)
\(=\dfrac{5}{8}\times\left(4+\dfrac{4}{5}\right)\)
\(=\dfrac{5}{8}\times\dfrac{24}{5}\)
\(=\dfrac{24}{8}\)
\(=3\)

a/Diện tích kính để làm bể cá:
\(8,4\times8,4\times5=352,8\left(dm^2\right)\)
b/Thể tích nước nếu đổ đầy bể cá đó:
\(8,4\times8,4\times8,4=592,704\left(dm^3\right)=592,704\left(l\right)\)

\(\dfrac{8}{9}\times\dfrac{7}{18}=\dfrac{56}{162}=\dfrac{28}{81}\)

\(6-x=\dfrac{9}{4}-\dfrac{7}{8}\)
\(6-x=\dfrac{18}{8}-\dfrac{7}{8}\)
\(6-x=\dfrac{11}{8}\)
\(x=6-\dfrac{11}{8}\)
\(x=\dfrac{48}{8}-\dfrac{11}{8}\)
\(x=\dfrac{37}{8}\)
#DatNe

\(1\dfrac{2}{3}\)giờ > \(100,5\) giây
\(\dfrac{1}{12}\)tuần = \(840\) phút
Giải thích:
\(1\dfrac{2}{3}\) giờ = 100 phút = 6000 giây > 100,5 giây
\(\dfrac{1}{12}\)tuần = \(\dfrac{7}{12}\) ngày = \(14\) giờ = \(840\) phút
#DatNe

\(\dfrac{9}{4}\times\dfrac{15}{11}+\dfrac{3}{4}:\dfrac{11}{7}-\dfrac{3}{4}\times\dfrac{8}{11}\)
\(=\dfrac{3}{4}\times3\times\dfrac{15}{11}+\dfrac{3}{4}\times\dfrac{7}{11}-\dfrac{3}{4}\times\dfrac{8}{11}\)
\(=\dfrac{3}{4}\times\dfrac{45}{11}+\dfrac{3}{4}\times\dfrac{7}{11}-\dfrac{3}{4}\times\dfrac{8}{11}\)
\(=\dfrac{3}{4}\times\left(\dfrac{45}{11}+\dfrac{7}{11}-\dfrac{8}{11}\right)\)
\(=\dfrac{3}{4}\times4\)
\(=3\)

Chiều cao mảnh vườn:
\(12\times\dfrac{2}{3}=8\left(m\right)\)
Diện tích mảnh vườn:
\(12\times8=96\left(m^2\right)\)
#DatNe