SOLUTION: As a motorist approaches the turnpike, he travels at the rate of 20 miles per hour in street traffic. For the first mile on the turnpike he travels at the rate of 30 miles per hour

Question 615010: As a motorist approaches the turnpike, he travels at the rate of 20 miles per hour in street traffic. For the first mile on the turnpike he travels at the rate of 30 miles per hour and then covers the next mile in one minute. What is his average rate for the first three mile of this trip?
A)25 mph
B)30 mph
C)33 mph
D)36 2/3 mph
E)50 mph
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
As a motorist approaches the turnpike, he travels at the rate of 20 miles per hour in street traffic.
For the first mile on the turnpike he travels at the rate of 30 miles per hour and then covers the next mile in one minute.
What is his average rate for the first three mile of this trip?
:
A mile a minute, av speed of 60 mph
:
Let a = average speed for the 1st three miles
:
Write a time equation; time = dist/speed
:
+ + =
Multiply by 60a
60a* + 60a* + 60a* = 60a*
Cancel the denominators
3a + 2a + a = 180
6a = 180
a = 180/6
a = 30 mph
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