Swimming fish: There is a group of fish in the fish pond. For the first time, 300 fish were caught, and they were marked and put back into the fish pond. After a few days, 100 fish were caught again, and 6 fish were found to be marked. How many fish are there in the pond?
游动的鱼：鱼塘里有一批鱼，第一次捕上来300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6尾．问鱼塘里大约有多少尾鱼？
<gadget id="calculator">6 / 100</gadget>
<output>3/50 = around 0.06</output>

<gadget id="calculator">300 / (3/50)</gadget>
<output>5_000</output>

<result>5_000</result>