Chu vi mảnh vườn hình chữ nhật là 

(5,5+3,75).2=37(m)

Số hoa cần trồng là

37:\(\dfrac{1}{4}\)=148 (khóm hoa)

vậy số khóm hoa cần trồng là 148 khóm hoa.

\(\dfrac{1}{5}+\dfrac{4}{5}:x=0,75=\dfrac{4}{5}:x=0,75-\dfrac{1}{5}=\dfrac{4}{5}:x=\dfrac{11}{20}=x=\dfrac{4}{5}:\dfrac{11}{20}=x=\dfrac{11}{16}\)

\(x+\dfrac{1}{2}=1-x=2x+\dfrac{1}{2}=1=2x=1-\dfrac{1}{2}=2x=\dfrac{1}{2}=x=\dfrac{1}{2}:2=x=\dfrac{1}{4}\)

a)\(\dfrac{2}{3}\).\(\dfrac{5}{4}\)-\(\dfrac{3}{4}.\dfrac{2}{3}\)=\(\dfrac{2}{3}.\left(\dfrac{5}{4}-\dfrac{3}{4}\right)\)=\(\dfrac{2}{3}.\dfrac{1}{2}=\dfrac{1}{3}\)

b)\(2.\left(\dfrac{-3}{2}\right)^2-\dfrac{7}{2}=2.\dfrac{-9}{4}-\dfrac{7}{2}=\dfrac{-9}{2}-\dfrac{7}{2}=-8\)

c)\(\dfrac{-3}{4}.5\dfrac{3}{13}-0,75\).\(\dfrac{36}{13}\)=\(\dfrac{-3}{4}.\dfrac{65}{13}-\dfrac{3}{4}.\dfrac{36}{13}=\dfrac{-3}{4}.\left(\dfrac{65}{13}-\dfrac{36}{13}\right)=\dfrac{-3}{4}.2=\dfrac{-3}{2}\)