A bamboo pole is 50 meters long. The difference between inserting the bamboo pole into the well and inserting the bamboo pole upside down is 10 meters. How deep is the well?
一根竹竿长50米，竹竿插到井里和竹竿倒插到井里相差10米，井多深？
<gadget id="calculator">50 - 10</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>