Question

John leaves Washington D.C. at 8 a.m. in a car headed for Atlanta. For the first 4 hours of the 1000 kilometer trip, John is driving 125 km/h. If John’s average speed is 100 km/h for the rest of the trip, what time will he arrive in Atlanta?

Answer 1

First, calculate the distance traveled y John in the first 4 hours, as follow:

d = v·t = (125 km/h)(4 h) = 500 km

hence, John traveled 500 km at the first 4 hours.

Then, to complete the trip, John have to travel another 500 km (becasue the trip is 1000 km).

Next, calculate the time of the rest of the trip, as follow:

t' = d'/v' = (500 km)/(100 km/h) = 5 h

then, John will take another 5 hours to complete the trip.

The total time of the trip was 4h + 5h = 9h, then, if John left Washington D.C. AT 8 a.m, he will arrive at 8 + 9 = 17h in Atlanta, or at 5 p.m.