9.25 On a bookshelf, 30 volumes can fit. In how many ways can they be arranged so that the first and second volumes do not stand next to each other?
9.25 Removing the first volume, we get 29! permutations of the books. The first volume can be placed next to the second in two ways; therefore, in 2 * 29! cases, the first and second volumes are next to each other. Since there are a total of 30! permutations, in 30! - 2 * 29! of them, the first and second volumes are not next to each other.

Answer: 28 * 29! ways.