Average speed = Total distance ÷ Total time (including dwells).
• Total distance = 60 km.
• Driving times:
• Segment 1: 20 ÷ 60 = \(\frac{1}{3}\) h
• Segment 2: 20 ÷ 120 = \(\frac{1}{6}\) h
• Segment 3: 20 ÷ 30 = \(\frac{2}{3}\) h
• Total driving time = \(\frac{1}{3} + \frac{1}{6} + \frac{2}{3} = \frac{7}{6}\) h.
• Total dwell time = 3 × 10 min = 30 min = \(\frac{1}{2}\) h.
• Total time = \(\frac{7}{6} + \frac{1}{2} = \frac{7}{6} + \frac{3}{6} = \frac{10}{6} = \frac{5}{3}\) h.
• Average speed = 60 ÷ \(\frac{5}{3}\) = 60 × \(\frac{3}{5}\) = 36 km/h.
Final Answer: 36 km/h