A frog eats 80 pests every day, 20 less than twice as much as a swallow. How many pests does a swallow eat every day?
一只青蛙每天吃80只害虫，比一只燕子吃的2倍少20只，一只燕子每天吃多少只害虫？
<gadget id="calculator">80 + 20</gadget>
<output>100</output>

<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<result>50</result>