Alright, this is kind of physics and kind of calculus. You don't have to give me the actual answer, I just would like to know how to get started.

A marching army column is 1km long. A courier is sent running from the column's rear to the front with a message, and is immediately sent back to the rear with a reply. During the time the courier is running, the column marches 10km. How far does the courier run?

Question

Alright, this is kind of physics and kind of calculus.  You don't have to give me the actual answer, I just would like to know how to get started.

A marching army column is 1km long.  A courier is sent running from the column's rear to the front with a message, and is immediately sent back to the rear with a reply.  During the time the courier is running, the column marches 10km.  How far does the courier run?

anonymous · Answer

First just ignore that marching army isn't moving (you choose marching army's reference frame). In that frame, the courier traveled with same speed either when sent to front or to rear. Is this enough?