A European roulette wheel has 18 red pockets, 18 black… and one green zero. Betting on red therefore wins only 18 times out of 37, giving the house an edge of about 2.7%. On a single bet, it's invisible; over millions of bets, the law of large numbers turns that sliver into near-certain income. The casino isn't gambling: it's collecting an average.
How many different structures can you build with six classic 2-by-4 Lego bricks of the same colour? The company used to quote just over 102 million. In 2005, Danish mathematician Søren Eilers recounted everything by computer: 915,103,765 combinations. The official estimate had been too low by a factor of about nine.
Fold an A4 sheet in half and you get an A5 with the same proportions. That only works for one ratio between length and width: about 1.414, the square root of 2. The A0 format measures exactly one square metre, and A4 is a sixteenth of it. With standard 80-gram-per-square-metre paper, an A4 sheet therefore weighs exactly 5 grams.