An island contained chameleons of three different colours: red, green and yellow. The chameleons were studied by some biologists and they found that when two chameleons of different colours met they changed their colours to the third one. They found that there were 2000 red chameleons and 3000 green ones on the day they counted them. They didn't get time to count the number of yellow chameleons.
When the biologists returned to the island 2 years later they found that all chameleons were red in colour. They were certain that no chameleons died because they did not find dead remains of any chameleon. What does it say about the number of yellow chameleons on the day the biologists counted the number of red and green chameleons?