physics
posted by zac .
An 18yearold runner can complete a 10.0 km course with an average speed of 4.51 m/s. A 50yearold runner can cover the same distance with an average speed of 4.31 m/s. How much later (in seconds) should the younger runner start in order to finish the course at the same time as the older runner?

The older runner requires 10,000/4.31 = 2320.2 s and the younger one requires
10,000/4.51 = 2217.3 s
The difference is 102.9 s. That is the head start required for them to finish at the same time.