\(\text{Dọc theo chiều dài, ta trồng được:}\)

\(5,5\div\dfrac{1}{4}=22(khómhoa)\)

\(\text{Dọc theo chiều rộng, ta trồng được:}\)

\(3,75\div\dfrac{1}{4}=15(khómhoa)\)

\(\text{Số khóm hoa cần trồng:}\)

\([(22+15)\times2]-4=70\)\((khómhoa)\)

\(\text{Vậy số khóm hoa cần trồng là 70}\)

a) \(\dfrac{1}{5}+\dfrac{4}{5}\div x=0,75\\ \)

\(\dfrac{4}{5}\div x=0,75-\dfrac{1}{5}\)

\(\dfrac{4}{5}\div x=\dfrac{11}{20}\)

\(x=\dfrac{4}{5}\div\dfrac{11}{20}\)

\(x=\dfrac{16}{11}\)

Vậy x=\(\dfrac{16}{11}\)

b) \(x+\dfrac{1}{2}=1-x\)

\(2x=1-\dfrac{1}{2}\)

\(2x=\dfrac{1}{2}\)

\(x=\dfrac{1}{2}\div2\)

\(x=\dfrac{1}{4}\)

Vậy x=\(\dfrac{1}{4}\)

a)\(\dfrac{2}{3}\times\dfrac{5}{4}-\dfrac{3}{4}\times\dfrac{2}{3}=\dfrac{2}{3}\times(\dfrac{5}{4}-\dfrac{3}{4})=\dfrac{2}{3}\times\dfrac{1}{2}=\dfrac{1}{3}\)

b)\(2\times(-\dfrac{3}{2})^2-\dfrac{7}{2}=2\times\dfrac{9}{4}-\dfrac{7}{2}=\dfrac{9}{2}-\dfrac{7}{2}=2\)

c)\(-\dfrac{3}{4}\times5\dfrac{3}{13}-0,75\times\dfrac{36}{13}=-\dfrac{51}{13}-\dfrac{27}{13}=-6\)