Giải:

Chu vi mảnh vườn là: (5,5 + 3,75).2 = 18,5(m)

Số khóm hoa cần trồng là: 18: \(\frac{1}{4}\) = 74(khóm hoa)

 \(a)\frac{1}{5}+\frac{4}{5}:x=0,75;\frac15+\frac45:x=\frac34;\frac45:x=\frac34-\frac15=\frac{11}{20};x=\frac45:\frac{11}{20}=\frac{16}{11}\)

b) \(x+\frac12=1-x;x+x=1-\frac12;2x=\frac12;x=\frac12:2=\frac12.\frac12=\frac14\)

a) \(\frac{2}{3}.\frac{5}{4}-\frac{3}{4}.\frac{2}{3}=\frac53.\frac24-\frac33-\frac24=\frac24.\left(\frac53-\frac33\right)=\frac24.\frac23=\frac13\)

b) \(2.\left(\frac{- 3}{2}\right)^2-\frac{7}{2}=2.\left(\frac94\right)-\frac72=\frac92-\frac72=1\)

c) \(-\frac{3}{4}.5\frac{3}{13}-0,75.\frac{36}{13}=\frac34.\frac{-68}{13}-\frac34.\frac{36}{13}=\frac34.\left(\frac{-68}{13}-\frac{36}{13}\right)=\frac34.\left(-8\right)=-6\)