Analysis: This question is an equal probability of possible events. The experiment involved randomly placing five books on a shelf, with 55 results. The event that meets the conditions is that the books in the same subject are not adjacent, indicating the result and getting the probability.

Solution: From the meaning of the problem, we know that the problem is the probability of an equal possible event.

The event involved in the experiment is that five books are randomly placed on a bookshelf, and there are A55= 120 results.

Quantitative study on non-adjacent arrangement methods of similar books under lower classification

Assuming that the first book is a Chinese book (or a math book) and the second book is a math book (or a Chinese book), there are 4×2×2×2× 1=32 possibilities;

Assuming that the first book is a Chinese book (or a math book) and the second book is a physics book, there are 8 possibilities: 4×12×1×1=;

Assuming that the first book is a physics book, there are1× 4× 2×1×1= 8 possibilities.

∴ The probability that books in the same subject are not adjacent P=48/120 =2 /5.

Comments: This topic examines the probability of possible events, which is a basic topic. This topic is a multiple-choice question in Zhejiang Volume Department. This topic can appear as a multiple-choice question or a fill-in-the-blank question, or as an answer question.