Book Cricket

let it fall open. the last digit is your runs.

the textbook under the desk: flop it open, the last digit of the page is your runs, a zero is out, and the pencil keeps the score

Book cricket is played with a textbook under the desk: you let it fall open, read the page number, and the last digit is your runs -- a 0 is out, six balls to an over, and somebody keeps the tally in pencil in the back of a notebook. You read the left-hand page, and every ordinary book numbers its left page even, so an innings is built only out of 2, 4, 6, 8 and the 0 that ends it; an odd number never comes up, and most people who played this for years never noticed. The book does not open at random either -- it falls open where the spine has been worn soft, which is why the same stretch of pages keeps coming back, and why the two halves of the open book keep settling to the same thickness.

Concepts: randomness, bias, parity.

An interactive you play with one thumb, on Wundr.