Let us say that:
A = slower car at 55mi/h
B = faster car at 65mi/h
1. Calculate time travelled of each car
A = 15 mi / (55mi/h) = 0.27 h
B = 15 mi / (65mi/h) = 0.23 h
Therefore:
0.23 – 0.27 = 0.04 h = 2.52 minutes
The faster car arrived sooner at 0.04 hours or 2.52 minutes
2. To get a 15 minute lead or 0.25h lead:
(x / 65) – (x / 55) = -0.25
x = -0.25 / (1/65 – 1/55)
x = 89.375 miles
The faster car has to travel 89.375 miles to have 15-min lead.
