Question

an 18 year old runner can complete a course in 13.8km with an average speed of 4.58m/s a 50 year old runner can cover the same distance with an average speed of 3.97m/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

Answer 1

$$t=t_2-t_1=\frac{s}{v_2}-\frac{s}{v_1}$$

$$t=\frac{13800}{3.97}-\frac{13800}{4.58}=463\ s$$