dọc theo chiều dài , ta trồng được số khóm hoa là :

5.5:\(\dfrac{1}{4}\)=22(khóm hoa)

Dọc theo chiều rộng , ta trồng được số khóm hoa là:

3,75:\(\dfrac{1}{4}\)=15(khóm hoa)

Số khóm hoa cần trồng là:

\(\left[\left(22+15\right).2\right]-4\)=70(khóm hoa)

vậy số khóm hoa cần trồn là70 khóm hoa.

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

\(\dfrac{1}{5}+\dfrac{4}{5}\):x=\(\dfrac{3}{4}\)

\(\dfrac{4}{5}\):x=\(\dfrac{3}{4}-\dfrac{1}{5}\)

\(\dfrac{4}{5}\).\(\dfrac{1}{x}\)=\(\dfrac{15}{20}-\dfrac{4}{20}\)

\(\dfrac{4}{5}.\dfrac{1}{x}=\dfrac{11}{20}\)

\(\dfrac{1}{x}=\dfrac{11}{20}:\dfrac{4}{5}\)

\(\dfrac{1}{x}=\dfrac{11}{20}.\dfrac{5}{4}\)

\(\dfrac{1}{x}=\dfrac{55}{80}\)=\(\dfrac{11}{16}\)

suy ra,x bằng:

11x=1.16

11x=16

x=16:11

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

vậy x=\(\dfrac{16}{11}\).

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

suy ra , x bằng :

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

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

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

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

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

vậy x=\(\dfrac{1}{4}\).

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

b)2.\(\left(\dfrac{-3}{2}\right)^2\)-\(\dfrac{7}{4}\)=2.\(\dfrac{9}{4}\)-\(\dfrac{7}{2}\)=\(\dfrac{2}{2}\)=1

c)-\(\dfrac{3}{4}\).\(5\dfrac{3}{13}\)-0,75.\(\dfrac{36}{13}\)=\(\dfrac{-3}{4}\).\(\dfrac{68}{13}\)-\(\dfrac{3}{4}\).\(\dfrac{36}{13}\)=\(\dfrac{-3}{4}\).\(\left(\dfrac{68}{13}+\dfrac{36}{13}\right)\)=\(\dfrac{-3}{4}\).\(\dfrac{104}{13}\)=\(\dfrac{-3}{4}\).8=-6