A set of tables and chairs costs 100 yuan, and it costs 1,200 yuan to buy 20 tables. How much is each chair?
一套桌椅100元，买20张桌子花了1200元，每把椅子多少元？
<gadget id="calculator">1_200 / 20</gadget>
<output>60</output>

<gadget id="calculator">100 - 60</gadget>
<output>40</output>

<result>40</result>