project can be completed by team A and team B alone in 4 days and 5 days respectively. If the two teams work together in one day, how much of the project can be completed.
一项工程，甲队与乙队单独做，分别要4天和5天才能完成，如果两队合做一天，可完成这项工程的多少．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) + (1/5)</gadget>
<output>9/20 = around 0.45</output>

<result>9/20 = around 0.45</result>