A project takes A 10 hours to complete and B takes 8 hours to complete. How many hours will it take A and B to complete it together?
一项工程，甲需10小时完成，乙需8小时完成，甲、乙合做需多少小时完成．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/10) + (1/8)</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>