There is a group of fish in the fish pond, 200 fish were caught for the first time, marked and put back into the fish pond, after a few days, 100 fish were caught again, and 5 fish were found with marks, how many fish are in the fish pond.
鱼塘里有一批鱼，第一次捕上来200尾，做好标记后放回鱼塘，数日后再捕上100尾，发现有标记的鱼为5尾，问鱼塘里大约多少尾鱼．
<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">200 / (1/20)</gadget>
<output>4_000</output>

<result>4_000</result>