\[\boxed{\mathbf{173.}}\]
\[Увеличить\ на\ 200:\]
\[300 + 200 = 500\]
\[400 + 200 = 600\]
\[500 + 200 = 700\]
\[600 + 200 = 800\]
\[700 + 200 = 900\]
\[800 + 200 = 1000\]
\[Уменьшить\ на\ 200:\]
\[300 - 200 = 100\]
\[400 - 200 = 200\]
\[500 - 200 = 300\]
\[600 - 200 = 400\]
\[700 - 200 = 500\]
\[800 - 200 = 600\]