A frog eats 80 pests every day, 20 less than twice as many as a swallow. How many pests does a swallow eat every day? (column equation solution)
一只青蛙每天吃害虫80只，比一只燕子的2倍少20只，一只燕子每天吃害虫多少只？(列方程解答)
<gadget id="calculator">80 + 20</gadget>
<output>100</output>

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

<result>50</result>