chu vi của mảnh vườn : 

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

số khóm hoa cần trồng: 

18,5 : \(\frac{1}{4}\)   = 74 (cây)

a, 4/5 : x = 3/4 - 1/5

4/5: x = 15/20-4/20

4/5 : x = 11/20

x= 11/20: 4/5

x= 11/20 : 16/20

x= 11/20. 20/16

x= 11/16

b, x + 1/2 +x = 1

x+x = 1 - 1/2

2x = 1/2

x = 1/2 : 2

x = 1/4

a, 4/5 : x = 3/4 - 1/5

4/5: x = 15/20-4/20

4/5 : x = 11/20

x= 11/20: 4/5

x= 11/20 : 16/20

x= 11/20. 20/16

x= 11/16

b, x + 1/2 +x = 1

x+x = 1 - 1/2

2x = 1/2

x = 1/2 : 2

x = 1/4

a, 2/3. (5/4 -3/4)

= 2/3.1/2

=1/3

b,2. 9/4 -7/2

=9/2-7/2

=1

c, -3/4 .68/13-0,75.36/13

=0,75 . (68/13-36/13)

= 3/4. 32/12

=96/48