\[\boxed{\text{П.82.}}\]
\[\textbf{а)}\ 435 + 23 \cdot 86 < 2\ 500\ \]
\[435 + 1\ 978 < 2\ 500\]
\[2\ 413 < 2\ 500.\]
\[171 \cdot (809 - 109) > 118\ 700\]
\[171 \cdot 700 > 118\ 700\]
\[119\ 700 > 118\ 700.\ \]