Book's page

Book pages can be very helpful to cast I Ching hexagrams. Russell Cottrell devised a simple method that uses even book's pages. Directly from his post on Clarity:

1. Fan the pages of a book (such as the I Ching).
2. Very casually divide the pages at a random position, as if cutting a deck of cards.
3. Look at the last two digits of the number of the even-numbered page (generally on the left).
4. If it is divisible by four, count it as “tails” or 2.
5. If not, count it as “heads” or 3.
6. To make the math easier, subtract a multiple of 4 from the page number, such as 40 or 80.
7. Three divisions determine one line, just like using coins.

[...] The edges of the pages must be fairly clean and smooth, without irregularities that could throw off the results.

Probabilities

As Russel suggested, the probabilities are the same as the three coins method. In fact, picking at random an even number, the chance of it being divisible by 4 is 1/2 and hence:

Prob(6) = Prob(9) = ¹/₈ = 12.5%
Prob(8) = Prob(7) = ³/₈ = 37.5%
Prob(yin) = Prob(yang) = ¹/₂