A's work efficiency is (1/9). B's is (1/10). How many days will it take for A and B to start working together?
甲的工作效率是(1/9)．乙的是(1/10)．甲、乙两人合作开工几天完成？
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/9) + (1/10)</gadget>
<output>19/90 = around 0.211111</output>

<gadget id="calculator">1 / (19/90)</gadget>
<output>90/19 = around 4.736842</output>

<result>90/19 = around 4.736842</result>