\(P=\dfrac{2}{3}+\dfrac{1}{4}+\dfrac{3}{5}-\dfrac{7}{45}+\dfrac{5}{9}+\dfrac{1}{12}+\dfrac{1}{35}\)

  \(=\left(\dfrac{2}{3}+\dfrac{1}{4}+\dfrac{1}{12}\right)+\left(\dfrac{3}{5}+\dfrac{1}{35}\right)+\left(\dfrac{-7}{45}+\dfrac{5}{9}\right)\)

\(=\dfrac{5}{6}+\dfrac{22}{35}+\dfrac{2}{5}=1\dfrac{181}{210}\)

\(Q=5-\dfrac{3}{4}+\dfrac{1}{5}-6-\dfrac{7}{4}+\dfrac{8}{5}-2+\dfrac{5}{4}+\dfrac{16}{5}\)

\(=\left(5-6-2\right)+\left(\dfrac{-3}{4}-\dfrac{7}{4}+\dfrac{5}{4}\right)+\left(\dfrac{1}{5}+\dfrac{8}{5}+\dfrac{16}{5}\right)\)

\(=\left(-3\right)+\dfrac{-5}{4}+5=-4\dfrac{1}{4}+5=\dfrac{3}{4}\)

\(A=\dfrac{1}{3}-\dfrac{8}{15}-\dfrac{1}{7}+\dfrac{2}{3}+\dfrac{-7}{15}+1\dfrac{1}{7}\)

\(=\left(\dfrac{1}{3}+\dfrac{2}{3}\right)+\left(\dfrac{-8}{15}+\dfrac{-7}{15}\right)+\left(\dfrac{-1}{7}+1\dfrac{1}{7}\right)\)

\(=1+\left(-1\right)+1\)

\(=0+1=1\)

\(B=0,25+\dfrac{3}{5}-\dfrac{1}{8}+\dfrac{2}{5}-1\dfrac{1}{4}\)

\(=\left(0,25-1\dfrac{1}{4}\right)+\left(\dfrac{3}{5}+\dfrac{2}{5}\right)-\dfrac{1}{8}\)

\(=-1+1-\dfrac{1}{8}\)

\(=2-\dfrac{1}{8}=\dfrac{15}{8}\)

Chu vi của mảnh vườn là :

           \(\left(5,5+3,75\right)\times2=18,5\left(m\right)\)

Số khóm hoa cần trồng là :

            \(18,5\div\dfrac{1}{4}=74\left(khómhoa\right)\)

\(\dfrac{1}{5}+\dfrac{4}{5}\div x=0,7\)

\(\dfrac{4}{5}\div x=0,7-\dfrac{1}{5}=0,5\)

\(x=0,5\div\dfrac{4}{5}=\dfrac{5}{8}\)

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

I would like a cake and some mineral water 

Art is my favourite subject

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

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)\(-\dfrac{3}{4}.5\dfrac{3}{13}-0.75.\dfrac{36}{13}=\dfrac{3}{4}.-\dfrac{68}{13}-\dfrac{3}{4}.\dfrac{36}{13}=\dfrac{3}{4}.\left(-\dfrac{68}{13}-\dfrac{36}{13}\right)=\dfrac{3}{4}.-8=-6\)