What is the average speed?

Question

Mr. Kent drove to a conference. The first half (in terms of distance) of the trip took 3 hours due to traffic. Traffic let up for the second half of the trip and he was able to increase his average speed by 20 mph to make sure he got there on time. Find his average rates of speed if he traveled for two hours at the second rate.

Answer 1

Recall the distance, rate and time equation. That is, distance=rate*time. Let's say Mr. Kent traveled x mph and it took 3 hours to get there halfway. So he went x+20 mph for 2 hours to go the remaining half (3x). This means:

2(x+20)=3x

2x+40=3x

40=x

 

To check our work:

If Mr. Kent traveled 40mph for three hours to get there halfway he traveled 40*3=120 miles. To travel the remaining 120 miles, he traveled 40+20=60mph for two hours or 60*2=120. Check!