1. Buratino left Papa Carlo's house and arrived at the Field of Wonders exactly at $22:00$. If his walking speed had been $25\%$ faster, he would have arrived at $21:30$. At what time did he leave the house?
Answer: at 19:30.

Solution: If Buratino spent $t$ (hours) on his journey, then with the increased speed, he would have spent 1.25 times less, i.e., $\frac{4}{5} t$. Therefore, he would have saved $\frac{1}{5} t$, which amounted to 30 minutes. Thus, he spent 2.5 hours on the way to the Field of Wonders, and he left home at 19:30.

Grading criteria: Correct and justified solution - 7 points, incorrect solution or only answer - $\mathbf{0}$ points.