\[\boxed{\mathbf{55.}}\]
\[350 - 50 = 300\]
\[630 - 30 = 600\]
\[820 - 20 = 800\]
\[170 - 70 = 100\]
\[203 - 3 = 200\]
\[405 - 5 = 400\]
\[704 - 4 = 700\]
\[309 - 9 = 300\]
\[180 - 100 = 80\]
\[510 - 500 = 10\]
\[920 - 900 = 20\]
\[460 - 400 = 60\]
\[208 - 200 = 8\]
\[409 - 400 = 9\]
\[702 - 700 = 2\]
\[601 - 600 = 1\]