You will need:
1. Walk through your garden and find 10 garden snails
2. Place a small dab of paint on their shell. This is harmless to the snail
3. Release the snails at different places in your garden
4. 1 week later, walk around your garden to find some more snails.
5. Use the formula below to work out the approximate number of snails in your garden.
Total population = Total number snails marked X Total number of snails in new sample group
Number of snails marked in a new sample group
If you found 20 snails with 5 being marked, this means you have recaptured half of your original group of 10 marked snails.
So the total population must be approximately 40 snails.
This answer is only a good guess, as anything could have happened to the snails over a week!