Four cars travel at constant speed along a road. Three of them (A, B and C) travel in one direction, and the fourth, D, in the opposite direction.

Car A passes B and C at 9:00h and 10:00h, respectively, and crosses car D at 11:00h.

Car D crosses car B and car C at 13:00h and 15:00h, respectively.

At what time did car B pass car C?

Bonus point: can you solve this geometrically?

(In reply to Geometric Solution by Robby Goetschalckx)

Good work, Robby. Maybe your graphic can be a little bit simplified if you make all speeds relatives to a car. I made speed of car C = 0, and its trajetory is an horizontal line. The point where the line of the car B crosses the line of the car C became the "centroid" of a triangle, as you found. 

Posted by pcbouhid on 2008-06-10 09:07:29