Physic word problem?

Question

You are to drive to an interview in another town, at a distance of 300km on an expressway. The interview is at 11:15 am. You plan to drive at 100km/h so you leave at 8:00am to allow some extra time. You drive at that speed for the first 100km, but then construction work forces you to slow to 40km/h for 40km. What would be the least speed needed for the rest of the trip to arrive in time for the interview?

I gave this problem a shot and figure out I drove at 100km/h and did this for the first 100km. I figured I already drove two hours for a total of 140km. This leaves me with 1:15min and 160km left to drive. Am I correct? If so where do I go from here? If not where did I go wrong? Please explain.

Answer 1

All correct so far - you are left with 160km to go and "one and a quarter hours" to do it in.

Speed = distance / time, so

Final speed = 160 / 1.25 = 128km/h

Answer 2

Yup...you got it.

: )