A batch of goods is stored, used up in 8 hours by car A, used up in 10 hours by car B, and now it takes 2.5 hours for the two cars, what fraction of the remaining goods is useless?
存放一批货物，用甲汽车8小时用完，用乙汽车10小时用完，现在两汽车用时用2.5小时，还剩这批货物的几分之几没有用？
<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>