During the school sanitation inspection, 18 classes were rated as "excellent", and the remaining 2 classes were rated as "good". What is the excellent rate?
学校卫生检查时，有18个班被评为"优秀"，其余的2个班被评为"良好"，优秀率是多少．
<gadget id="calculator">18 + 2</gadget>
<output>20</output>

<gadget id="calculator">18 / 20</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">(9/10) * 1</gadget>
<output>9/10 = around 0.9</output>

<result>9/10 = around 0.9</result>