\[\boxed{\text{100.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[140\ :20 = 140\ :(2 \cdot 10) =\]
\[= (140\ :10)\ :2 = 14\ :2 = 7.\]
\[560\ :7 = 80.\]
\[8\ 100\ :900 =\]
\[= 8\ 100\ :(9 \cdot 100) =\]
\[= (8\ 100\ :100)\ :9 =\]
\[= 81\ :9 = 9.\]
\[3\ 200\ :800 =\]
\[= 3\ 200\ :(8 \cdot 100) =\]
\[= (3\ 200\ :100)\ :8 = 32\ :8 = 4.\]
\[500 + (600 - 3 \cdot 100)\ :10 =\]
\[= 500 + (600 - 300)\ :10 =\]
\[= 500 + 300\ :10 = 500 + 30 =\]
\[= 530.\]
\[9\ 000\ :(100 - 90)\ :9 \cdot 2 =\]
\[= 9\ 000\ :10\ :9 \cdot 2 =\]
\[= 900\ :9 \cdot 2 = 100 \cdot 2 = 200.\ \]