A project alone takes 9 hours and B alone takes 12 hours. If A works for 1 hour first, then B takes over from A for 1 hour, and then A takes over from B for 1 hour...the two work alternately in this way, how many hours will it take to complete the task?
一项工程，甲独做需9小时，乙独做需12小时．如果甲先做1小时，然后乙接替甲做1小时，再由甲接替乙做1小时…两人如此交替工作，完成任务共用多少小时？
<gadget id="calculator">2 * 5</gadget>
<output>10</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/9) + (1/12)</gadget>
<output>7/36 = around 0.194444</output>

<gadget id="calculator">(7/36) * 5</gadget>
<output>35/36 = around 0.972222</output>

<gadget id="calculator">1 - (35/36)</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">(1/36) / (1/9)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">10 + (1/4)</gadget>
<output>41/4 = around 10.25</output>

<result>41/4 = around 10.25</result>