20. Вычислите: 4/3 + (−5 1/2 + 5/4 · 3 1/5) : 9/10.

\[5\frac14\cdot3\frac15=\frac{21}{4}\cdot\frac{16}{5}=\frac{84}{5}.\]

\[-5\frac12+\frac{84}{5}=-\frac{11}{2}+\frac{84}{5}=\frac{113}{10}.\]

\[\frac{113}{10}:\frac9{10}=\frac{113}{9}.\]

\[\frac43+\frac{113}{9}=\frac{12+113}{9}=\frac{125}{9}.\]

Ответ: \(\frac{125}{9}\).