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Counting Fish

Age 14 to 16
Challenge Level

Image (c)

I need a figure for the fish population in a lake.

I catch 40 fish and mark a scale on each fish so that they can be identified if caught again.

The fish are then released and one week later I once more catch 40 fish and look to see which of these I caught before.

How does this help me come up with a figure for the fish population in a lake?

What assumptions does this method of estimating the fish population rely on?
How do you think you could improve the accuracy of your estimate?

Click here for a poster of this problem.

This resource is part of the collection Statistics - Maths of Real Life