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

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

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

         \(\dfrac{4}{5}\) : 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

   X+\(\dfrac{1}{2}\)  = -X+1

   X+\(\dfrac{1}{2}\) - \(\dfrac{1}{2}\)= -X+1-\(\dfrac{1}{2}\)

   X = -X+\(\dfrac{1}{2}\)

   X+X=-X+\(\dfrac{1}{2}\) +X

   2X = (-X+X)+\(\dfrac{1}{2}\)

   2X = \(\dfrac{1}{2}\)

     X = \(\dfrac{1}{2}\) : 2

     X = \(\dfrac{1}{4}\)

Vậy X = \(\dfrac{1}{4}\)

Chu vi mảnh vườn là:

     (5,5 + 3,75).2 = 18,5 (m)

Số khóm hoa cần trồng là:

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

Vậy cần trồng 74 khóm hoa.

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

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

= \(\dfrac{2}{3}\).\(\dfrac{1}{2}\)

= \(\dfrac{1}{3}\)

b) 2.(\(\dfrac{-3}{2}\))\(^2\) - \(\dfrac{7}{2}\)

=2.\(\dfrac{9}{4}\) - \(\dfrac{7}{2}\)

=\(\dfrac{9}{2}\)-\(\dfrac{7}{2}\)

=\(\dfrac{2}{2}\) = 1

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

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

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

=\(\dfrac{3}{4}\).[(\(\dfrac{-68}{13}\))-\(\dfrac{36}{13}\)]

=\(\dfrac{3}{4}\).(\(\dfrac{-104}{13}\))

= -6