For a manuscript, A can finish typing in 12 hours alone, and B can finish typing in 15 hours alone. A and B worked together for half an hour, how much of this manuscript was completed.
一份稿件，甲单独打12小时完成，乙单独打15小时完成．甲与乙合做了半小时，共完成这份稿件的多少．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(3/20) * (1/2)</gadget>
<output>3/40 = around 0.075</output>

<result>3/40 = around 0.075</result>