project can be completed by team A alone in 10 days and team B alone in 8 days. How many days will it take for teams A and B to work together to complete the entire project (9/10).
一项工程，甲队单独做10天完成，乙队单独做8天完成，甲乙两队合做多少天完成全部工程的(9/10)．
<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<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">(9/10) / (9/40)</gadget>
<output>4</output>

<result>4</result>