The article analyzes our experience of teaching the subject combinatorics and working with data at Trnava University, Faculty of Education before, during, and after the COVID-19 pandemic. During this period, the subject was taught in the form of blended learning, i.e., a combination of face-to-face (during the pandemic online) instruction and e-learning. The use of video lectures in the e-learning course was the main difference in teaching the subject before and after the pandemic. The author’s analysis is based on the results of 883 students over six academic years. The analysis of the results shows that the COVID-19 pandemic and the associated restrictions on face-to-face instruction had no negative impact on students’ knowledge. The analysis further shows that students’ performance in the post-pandemic period is statistically significantly better than in the pre-pandemic period, which was mainly due to the use of video lectures. The analysis of the final test results is consistent with the results of the questionnaire survey in which majority of students found the video lectures to be useful.