chu vi mảnh vườn này là :

( 5,5 + 3,75 ) . 2  = 18,5 (m)

Số khóm hoa cần trồng là : 

18,5 : \(\dfrac{1}{4}\) = 74 (khóm hoa)

Vậy cần trồng 74 khóm hoa dọc theo các cạnh của mảnh vườn

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

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

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

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

x= \(\dfrac{16}{11}\)

vậy x = \(\dfrac{16}{11}\)

b, x + \(\dfrac{1}{2}\) = 1 − x 

2x + \(\dfrac{1}{2}\) = 1 

2x          = 1 − \(\dfrac{1}{2}\)

x+12=1−x
x+12=1−xx+12=1−x

x+12=1−x2x          = \(\dfrac{1}{2}\)

x            =   \(\dfrac{1}{2}\) : 2

x            =    \(\dfrac{1}{4}\)
x+12=1−xx+12=1−x

 a, \(\dfrac{2}{3}\).(\(\dfrac{5}{4}\) − \(\dfrac{3}{4}\))

= \(\dfrac{2}{3}\) . \(\dfrac{2}{4}\) 

= \(\dfrac{2}{3}\).\(\dfrac{1}{2}\)

= \(\dfrac{2}{6}\)

=\(\dfrac{1}{3}\)

b, 2. \(\dfrac{9}{4}\) − \(\dfrac{7}{2}\) 

= \(\dfrac{18}{4}\) − \(\dfrac{7}{2}\) 

= \(\dfrac{18}{4}\) − \(\dfrac{14}{4}\) 

= 1

c, \(\text{−}\dfrac{3}{4}\) .5\(\dfrac{3}{13}\) − 0,75 . \(\dfrac{36}{13}\) 

= \(\text{−}\dfrac{3}{4}\).\(\dfrac{68}{13}\) − \(\dfrac{75}{100}\) . \(\dfrac{36}{13}\) 

=\(\text{−}\dfrac{3}{4}\).\(\dfrac{68}{13}\)− \(\dfrac{3}{4}\) . \(\dfrac{36}{13}\) 

= (−\(\dfrac{3}{4}\)) . (\(\dfrac{68}{13}\)−\(\dfrac{36}{13}\))

=(− \(\dfrac{3}{4}\)) . \(\dfrac{32}{13}\)

= −\(\dfrac{8}{5}\)