Processing a batch of parts, the master can complete it in 8 hours alone, the apprentice can complete it in 10 hours alone, and the master and apprentice can work together in 2.5 hours, how much is left unfinished?
加工一批零件，师傅独做8小时完成，徒弟独做10小时完成，师徒二人合做2.5小时，还有几分之几没有完成？
<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

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

<gadget id="calculator">(1/8) + (1/10)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">(9/40) * 2.5</gadget>
<output>0.5625</output>

<gadget id="calculator">1 - 0.5625</gadget>
<output>0.4375</output>

<result>0.4375</result>