1. A father and son measured the length of the courtyard with their steps in winter, starting from the same place and walking in the same direction. In some places, the father's and son's footprints coincided exactly. In total, there were 61 footprints along the measurement line on the snow. What is the length of the courtyard if the father's step is $0,72 \boldsymbol{\mu}$, and the son's step is 0.54 m?
1. Let's calculate the ratio of the father's step length to the son's step length, which is: $0.72: 0.54 = 4: 3$. Therefore, four steps of the son equal three steps of the father, and on such a segment, we get 6 footprints. In total, $(61-1): 6=10$ segments (Fig. 9). The length of the courtyard is $10 \cdot 3$ steps of the father or $10 \cdot 3: 0.72=21.6(m)$. Otherwise: $10 \cdot 4 \cdot 0.54 \doteq 21.6(m)$.