Question 109391
Jennie drives to her son's house in 5 hours when there is heavy traffic. When there is no traffic, the same trip takes 4 hours. She can drive an average of 12 m.p.h. faster when there is no traffic than when there is heavy traffic.
:
What is her average speed when there is no traffic?
:
Let s = Av speed, no traffic
Then
(s-12) = Av speed in traffic
:
The distance for both situations is given as the same:
:
Write a distance equation: Distance = time * speed
:
Dist traffic = Dist no traffic
5(s-12) = 4s
5s - 60 = 4s
5s - 4s = +60
s = 60 mph no traffic
and
60 - 12 = 48 mph in traffic
:
:
What is the distance from her house to her son's house?
5(48) = 240 miles
and
4(60) = 240 miles