Chapter 3: Problem 53
Let the distance travelled by car with \(42 \mathrm{~km} \mathrm{~h}^{-1}\) for 20 minutes be \(\mathrm{S}\), and distance travelled with 60 \(\mathrm{km} \mathrm{h}^{-1}\) for 30 minutes be \(\mathrm{S}_{2}\) \(\Rightarrow \mathrm{S}_{1}=42 \mathrm{~km} \mathrm{~h}^{-1} \times \frac{1}{3} \mathrm{~h}=14 \mathrm{~km}\) \(\Rightarrow \mathrm{S}_{2}=60 \mathrm{~km} \mathrm{~h}^{-1} \times \frac{1}{2} \mathrm{~h}=30 \mathrm{~km}\) Total distance \(\mathrm{S}=\mathrm{S}_{1}+\mathrm{S}_{2}=14+30=44 \mathrm{~km}\)