SOLUTION: Assume the distance b/w Washington DC and Philadelphia is 120 miles. Suppose on a recent trip, driving from DC to Philly, your average speed for the first half of the trip was 40

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Question 217360: Assume the distance b/w Washington DC and Philadelphia is 120 miles. Suppose on a recent trip, driving from DC to Philly, your average speed for the first half of the trip was 40 mph. If you wanted to average 50 mph for the entire trip, what must be the average speed for the second half of you trip?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Assume the distance b/w Washington DC and Philadelphia is 120 miles.
Suppose on a recent trip, driving from DC to Philly, your average speed for
the first half of the trip was 40 mph.
If you wanted to average 50 mph for the entire trip, what must be the average
speed for the second half of you trip?
:
let s = speed required to do this:
;
Write a time equation: Time = dist%2Fspeed
60%2F40 + 60%2Fs = 120%2F50
:
Multiply equation by 200s, results
5s(60) + 200(60) = 4s(120)
:
300s + 12000 = 480s
:
12000 = 480s - 300s
:
12000 = 180s
s = 12000%2F180
s = 662%2F3 mph to average 50 mph
;
;
Check solution
60%2F40 + 60%2F66.67 = 120%2F50
1.5 + .9 = 2.4