25 minutes. According to the query of Tencent classroom, I learned that Zhang Yu's Basic Theory of Probability 6 has been taught for 25 minutes. Zhang Yu, a well-known math tutor for postgraduate entrance examination in China, is the "backbone teacher of national excellent curriculum construction" of the Ministry of Education, the author of the national best-selling lectures on advanced mathematics 18 and classic questions on the origin of postgraduate entrance examination mathematics 1000, and the invited expert of the 2007 Slovenian Global Sustainable Development Conference. The "subject-source teaching method" was initiated, and the knowledge structure and system of postgraduate mathematics were completely interpreted. It has a strong ability to grasp and predict the propositions and review ideas of postgraduate mathematics, so that students can easily and efficiently win high marks.