\[\boxed{\mathbf{187.}}\]
\[420 + 300 = 300 + 420 = 720\]
\[650 + 200 = 850 > 650 + 2 =\]
\[= 652\]
\[500 + 43 = 543 > 4 + 500 =\]
\[= 504\]
\[600 - 500 =\]
\[= 100 < 630 - 500 = 130\]
\[742 - 40 = 702 > 742 - 42 =\]
\[= 700\]
\[808 - 8 = 800 > 808 - 800 = 8\]