A classmate has done 20 questions and got 15 correct, what is the error rate?
某同学做了20道题，做对了15道，错误率是多少．
<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">5 / 20</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) * 1</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>