Edit: 🤦🏻♂️ What a fail of a title. What I meant was…
How do we know what the population of animals are?
In: 7
The method I was taught in school was thus:
You go out and capture, at random, 20 kangaroos. You put a tag on all of them, then let them go. A few days later you capture another random 20 kangaroos. What percentage of the second batch are tagged? You can then extrapolate how many kangaroos there are in total using this percentage.
For example, if there were 5 tagged kangaroos in the second batch, that’s 25% of the total. We can then assume that the first batch was 25% of the total population. Thus, we estimate that there are (20 x 4) 80 kangaroos in this area.
Alternatively, lets say there was 2 tagged kangaroos in the second batch. That’s only 10% of the total. We would then say that the kangaroo population in this area is (20 x 10) 200.
[This page](https://thirdspacelearning.com/gcse-maths/statistics/capture-recapture/) goes into more detail on the maths involved.
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