1. Once in a physics and mathematics school, September was declared the month of information technology. Therefore, every Monday in September, there was 1 computer science lesson in each class, every Tuesday - 2 lessons, every Wednesday - 3 lessons, every Thursday - 4 lessons, and every Friday - 5 computer science lessons. Saturdays and Sundays were weekends in this school. On September 1st, there were ceremonial assemblies in the school, so there were no lessons. It is known that in total, 64 computer science lessons were held in each class throughout September. On which day of the week did September 1st fall that year? September has 30 days.
Answer: Wednesday.

Solution. In 1 full week, there are $1+2+3+4+5=15$ lessons. From September 2 to September 29 (28 days), 4 full weeks will pass, which is 60 lessons. Therefore, on September 30, there were $64-60=4$ lessons, meaning it was a Thursday. Thus, the Thursdays were $23, 16, 9$, and September 2, and September 1 was a Wednesday.

Criteria. Only the answer - 1 point. Noted that in 1 full week, there are 15 lessons, but no further progress or errors in the progress - 2 points. For an answer with verification (that the answer "Wednesday" fits) without proof that September 1 could not have been any other day of the week - no more than 3 points.