One link on one of the most frequent tags on this blog:
And on a (slightly) different note:
And to complete a trio (one for all, all for one), a sociological and ecological riddle with just a little bit of mathematics:
One man eats 1.9 meals a day and three rotis per meal. He leaves half a roti thrice a month, which gets thrown. Another man eats 2.9 meals a day and eight rotis per meal. He only leaves one roti once every three months, which he religiously feeds to a stray animal or to a beggar. Which one of the two men is more socially and ecologically responsible? The sizes and weights of the rotis remain the same for both.