An ecologist catches 100 frogs from a pond, marks them, and releases them back into the pond. after a few days, another 100 frogs are captured and 10 have the marks on them. how many frogs are in the pond?

There are 1,000 frogs in the pond. If the second time he captured 100 frogs, there were only 10 out of the original 100 that were marked, this would mean you would have to pull 900 more out to get all 90 marked out.