The school brings some money to buy study tables and chairs. With the money, you can buy 30 tables and 40 chairs. One table and two chairs are a set of tables and chairs. How many sets of tables and chairs can you buy with this money?
学校带一些钱买学桌和椅子，这些钱全买桌子可买30张，全买椅子可买40张，一张桌子和两张椅子是一套桌椅，这些钱能买多少套桌椅？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/30) + (1/40) + (1/40)</gadget>
<output>1/12 = around 0.083333</output>

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

<result>12</result>