Suppose some lions and lambs satisfy:

- There are at least two lions.
- Each lion has bitten at least three lambs.
- For any two lions, there is exactly one lamb that has been bitten by both.
- For any two lambs, there is at least one lion that has bitten both.
- One of the lions has bitten six lambs.

How many lions are there? How many lambs are there?

Source: Andy Liu, Univ. of Alberta

© Copyright 2001 Stan Wagon. Reproduced with
permission.