Car A and Car B get on the freeway at the same time and the same point. They are traveling at different speeds, but each car is maintaining its own consistent speed. After a few minutes, Car A is at mile marker 10 and Car B is at mile marker 17. When Car B reaches mile marker 85, at which mile marker is Car A? *
Let vA = constant speed of car A, mph. Let vB = constant speed of car B, mph.
After time t hours, car A reaches mile marker 10, so the time taken is t = 10/vA. At the same instant, car B reaches the mile marker 17, therefore t = 17/vB = 10/vA That is, vA/vB = 10/17.
When car B reaches the mile marker 85, the time taken is T = 85/vB. At the same time, car A reaches the mile marker given by x = T*vA = (85/vB)*vA = (vA/vB)*85. Because vA/vB = 10/17, therefore x = (10/17)*85 = 50.
When car B reaches the mile marker 85, car A reaches the mile marker 50.