Xiao Ming did 20 verbal calculations and got 18 correct. What is the error rate?
小明做20题口算，做对18题，错误率为多少．
<gadget id="calculator">20 - 18</gadget>
<output>2</output>

<gadget id="calculator">2 / 20</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) * 1</gadget>
<output>1/10 = around 0.1</output>

<result>1/10 = around 0.1</result>