Chiều dài đám đất hình chữ nhật là:

          \(60\) \(\times\) \(\dfrac{4}{3}\) = \(80\) \(\left(m\right)\)

     Diện tích đám đát hình chữ nhật là:

          \(60\) \(\times\) \(80\) = \(4800\) \((\)\(^{m^2}\)\()\)

     Diện tích trồng cây là:

          \(4800\)\(\times\) \(\dfrac{7}{12}\) = \(2800\)\((\) \(^{m^2}\)\()\)

     Diện tích phần đất còn lại là:

          \(4800\) \(-\) \(2800\) = \(2000\) \((\)\(^{m^2}\)\()\)

     Diện tích ao thả cá là:

          \(2000\) \(\times\) \(30\%\) = \(600\)\((\)\(^{m^2}\)\()\)

               Đáp số: \(600\) \(^{m^2}\).

a)

\(\dfrac{-5}{9}\) \(+\) \(\dfrac{8}{15}\)\(+\) \(\dfrac{-2}{11}\)\(+\) \(\dfrac{4}{-9}\)\(+\) \(\dfrac{7}{15}\)

= \(\dfrac{-5}{9}\)\(+\) \(\dfrac{8}{15}\)\(+\) \(\dfrac{-2}{11}\)\(+\)\(\dfrac{-4}{9}\)\(+\)\(\dfrac{7}{15}\)

= (\(\dfrac{-5}{9}\)\(+\)  \(\dfrac{-4}{9}\)) \(+\) ( \(\dfrac{8}{15}\)\(+\) \(\dfrac{7}{15}\))\(+\)  \(\dfrac{-2}{11}\)

=\(\left(-1\right)\) \(+1\) \(+\)  \(\dfrac{-2}{11}\)

= \(0+\) \(\dfrac{-2}{11}\)

= \(\dfrac{-2}{11}\)

b) (\(\dfrac{7}{2}\) \(\times\)  \(\dfrac{5}{6}\)) \(+\) (\(\dfrac{7}{6}\)  \(\div\)  \(\dfrac{2}{7}\))

=  \(\dfrac{35}{12}\)  \(+\)( \(\dfrac{7}{6}\) \(\times\) \(\dfrac{7}{2}\) )

= \(\dfrac{35}{12}\) \(+\) \(\dfrac{49}{12}\)

= \(\dfrac{84}{12}\)

= \(7\)

a)

\(\dfrac{-3}{8}\)= \(\dfrac{-3.3}{8.3}\) =\(\dfrac{-9}{24}\)

\(\dfrac{5}{-12}\) = \(\dfrac{-5}{12}\) = \(\dfrac{-5.2}{12.2}\) = \(\dfrac{-10}{24}\)

Vì \(\dfrac{-9}{24}\) > \(\dfrac{-10}{24}\) nên \(\dfrac{-3}{8}\) > \(\dfrac{5}{-12}\)

Vậy \(\dfrac{-3}{8}\) > \(\dfrac{5}{-12}\).

b)

\(\dfrac{3131}{5252}\)=\(\dfrac{3131:101}{5252:101}\) = \(\dfrac{31}{52}\)

\(\dfrac{31}{52}\) = \(\dfrac{31}{52}\)

Vì \(\dfrac{3131}{5252}\) = \(\dfrac{31}{52}\)và \(\dfrac{31}{52}\)= \(\dfrac{31}{52}\) \(\Rightarrow\) \(\dfrac{3131}{5252}\)= \(\dfrac{31}{52}\)

Vậy \(\dfrac{3131}{5252}\) = \(\dfrac{31}{52}\).