\[\boxed{\mathbf{166.}}\]
\[1)\ 600 + 200 = 800\]
\[600 - 200 = 400\]
\[2)\ 400 + 200 = 600\]
\[400 - 200 = 200\]
\[500 + 400 = 900\]
\[500 - 400 = 100\]
\[700 + 300 = 1000\]
\[700 - 300 = 400\]