Bài làm:

Đổi \(\dfrac{1}{4}\)m = 0,25m

Chu vi mảnh vườn hình chữ nhật là:

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

Số khóm hoa cần trồng là:

18,5 : 0,25 = 74 ( khóm hoa )

Vì 4 khóm hoa ở góc được tính 2 lần nên:

74 - 4 = 70 ( khóm hoa )

Vậy số khóm hoa cần trồng là 70 khóm hoa

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

<=> \(\dfrac{4}{5}\) : x = \(\dfrac{19}{20}\)

             x = \(\dfrac{4}{5}\):\(\dfrac{19}{20}\)

             x = \(\dfrac{16}{19}\)

b. x+\(\dfrac{1}{2}\) = 1-x

<=> x+\(\dfrac{1}{2}\)+x = 1

<=> x + x = 1 - \(\dfrac{1}{2}\)

       x = \(\dfrac{1}{4}\)

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

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

= \(\dfrac{2}{3}\)-\(\dfrac{1}{2}\)

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

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.\(\dfrac{36}{13}\)

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

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

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

=\(\dfrac{-24}{13}\)

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.\(\dfrac{36}{13}\)

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

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

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

=\(\dfrac{-24}{13}\)