## Task B-1.5.

During the French Revolution, there was an idea to divide the day (a period of 24 hours) into 10 hours, and each hour into 100 minutes. Although this idea did not catch on, in Marko's school, they sometimes use such a "decimal clock." When Marko started solving the problem on the "decimal clock," it was exactly 4.5 hours. When he finished, the "regular clock" showed exactly 11:15. Petra started solving the same problem at noon by "regular time," and finished at 5.2 hours on the "decimal clock." Who of the two solved the problem faster and by how much faster in "regular time"? (Note: time is measured from midnight on both clocks.)
## Solution.

Since 10 "decimal hours" correspond to 24 "regular hours", we conclude that 1 "decimal hour" is equal to 2.4 "regular hours".

Therefore, Marko started solving the problem at 4.5$\cdot$2.4 h $=10.8 \mathrm{~h}=10 \mathrm{~h} 48 \mathrm{~min}$ by "regular time".

Since Marko finished the problem at 11 h 15 min, we conclude that he spent 27 minutes solving the problem.

1 point

Furthermore, noon by "regular time" corresponds to the time of 5 "decimal hours", so we conclude that Petra finished the problem after 0.2 "decimal hours", i.e., 0.2 . $2.4=0.48 \mathrm{~h}=28.8 \mathrm{~min}$ by "regular time".

Therefore, it is evident that Marko solved the problem faster by 1.8 min.