A car travels 30 kph going uphill and 60 kph going downhill. What is its average speed if it goes 100 km uphill and 50 km downhill?
+51 The average speed equals \(\frac{total distance}{total time}\). The total time is the time going uphill + the time going downhill. This is \(\frac{100}{30}+\frac{50}{60} = \frac{125}{30}=\frac{25}{6}\). So the fraction\(\frac{total distance}{total time} = \frac{150}{\frac{25}{6}} = 150/25*6=\boxed{36}\)
