bài giải

           Chu vi mảnh vườn hình chữ nhật là : 

                       (5,5+3,75).2=18,5(m)

          Cần số khóm hoa là :

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

              Vậy cần trồng 74 khóm hoa

 a) \(\dfrac{1}{5}\)+\(\dfrac{4}{5}\): 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=\(\dfrac{16}{11}\)

            Vậy x=\(\dfrac{16}{11}\)

b) x+\(\dfrac{1}{2}\)=1-x

    x+ x=1-\(\dfrac{1}{2}\)

        2x=\(\dfrac{1}{2}\)

         x=\(\dfrac{1}{2}\):2

         x=\(\dfrac{1}{4}\)

     Vậy x=\(\dfrac{1}{4}\)

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

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

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