số khóm hoa cần trồng là:

[(5,5:0,25)+(3,75:0,25)] x 2-4=70(khóm)

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

    \(\dfrac{4}{5}\div x=0,75-\dfrac{1}{5}=0,55\)

    \(x=\dfrac{4}{5}\div0,55=\dfrac{16}{11}\)

b,\(x+\dfrac{1}{2}=1-x\)

   \(2x+\dfrac{1}{2}=1\)

   \(2x=1-\dfrac{1}{2}=\dfrac{1}{2}\)

   \(x=\dfrac{1}{2}\div2=\dfrac{1}{4}\)

a, \(\dfrac{2}{3}\cdot\dfrac{5}{4}-\dfrac{3}{4}\cdot\dfrac{2}{3}=\dfrac{2}{3}\cdot\left(\dfrac{5-3}{4}\right)=\dfrac{2}{3}\cdot\dfrac{1}{2}=\dfrac{1}{3}\)

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

c,\(\dfrac{-3}{4}\cdot5\dfrac{3}{13}-0,75\cdot\dfrac{36}{13}=-\dfrac{3}{4}\cdot\left(5\dfrac{3}{13}+\dfrac{36}{13}\right)=-\dfrac{3}{4}\cdot8=-6\)