Question

Three hundred fish are tagged and released into a pond. A month later 100 fish are caught and then released back into the same pond. Of those 100 fish caught only 15 had tags. How many fish are in the pond? Is the answer 2000 fish?

Answer 1

Assuming the 300 fish mix in randomly in the fish population, then the later catch would indicate that 15% of the fish were tagged.

So, .15n=300
n = 2000

you are correct.