Question

On a 120 km trip a motorist travels 60 km at 60 km/h. How fast must the motorist go for the next 60km in order to average 120km/h for the whole trip?

i have attempted this question, yet the answers say it is impossible.

Answer 1

Speed is distance traveled over time, or
v = d/t

Let x = time needed for the next 60 km

120 km/hr (average) = [(speed1) + (speed2)] / 2
120 = (60 + (60/t)) / 2
240 = 60 + 60/t
60/t = 240 - 60
60/t = 180 km/hr (speed2)

time needed to achieve this speed is
t = 60/180 = 1/3 hr

Answer 2

2 hours