A salesman drives from Otawa to Montreal. The first half of the distance of his journey, he drives at a constant speed of 80 km/h. The second half of the distance of his journey, he drives at a constant speed of 120 km/h.
What is the salesman's average speed for the complete journey?
96 km/h
Let the length of the journey be n km. The first half of the journey takes (1/2×n)/80 = 1/160×n hours, and the second half of the journey takes (1/2×n)/120 = 1/240×n hours. The average speed for the complete journey is n/(1/160×n+1/240×n) = 96 km/h.