A batch of wood can make 20 sets of tables and 30 sets of chairs. If one table and one chair count as one set, how many sets of such tables and chairs can this batch of wood make?
一批木材，如果只做桌子可以做20张，如果只做椅子可以做30张，如果1张桌子和1张椅子算一套，那么这批木材可以做这样的桌椅多少套？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>