CaptureRecapture The bear population in a certain wildlife r

Capture-Recapture: The bear population in a certain wildlife reserve was estimated as follows: 35 bears were captured, tagged and released. After some time 50 bears were captured and of these 22 were found to be tagged. The total bear population N was calculated then from the equation: 35/n = 22/50 ; yielding N to be approximately 80? mathematically explain how this works?

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