Proportions Math

Question

In a capture-recapture study, a biologist tagged and released 210 deer. A month later she captured 60 deer, 30 of which had tags. About how many deer were in the population?

Answer 1

deer population = 420 deer

210/420 = 30/60 = 1/2

1/2 where tagged, 1/2 of 420 = 210

1/2 of 60 = 30

assuming he got a random sample, and not a biased sample of deer

closer to the place where he released the tagged deer.