Walking and Cycling
They have a tandem bike on which they can travel at 25 km/h.
The tandem bike can be used by one person or two persons at a time but not three.
Regardless of the number of persons on the bike it maintains a speed of 25 km/h.
Find the minimal time for the THREE of them to reach a point 100 km away.
Assume no time loss starting, stopping or turning.