It takes 8 hours for an express train to travel from A to B, and 10 hours for a slow train to travel from B to A. Two trains depart from A and B oppositely at the same time. How many hours will they meet?
一列快车从甲地开往乙地需8小时，一列慢车从乙地开往甲地需10小时．两列火车同时从甲、乙两地相对开出，几小时相遇？
<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">1 / (9/40)</gadget>
<output>40/9 = around 4.444444</output>

<result>40/9 = around 4.444444</result>