Question 6
A biologist wants to calculate the number of fish in a lake. On May $1$ she catches a random sample of $60$ fish, tags them, and releases them. On September $1$ she catches a random sample of $70$ fish and finds that $3$ of them are tagged. To calculate the number of fish in the lake on May $1,$ she assumes that $25\%$ of these fish are no longer in the lake on September $1$ (because of death and emigrations), that $40\%$ of the fish were not in the lake May $1$ (because of births and immigrations), and that the number of untagged fish and tagged fish in the September $1$ sample are representative of the total population. What does the biologist calculate for the number of fish in the lake on May $1?$