SOLUTION: If you must average 60 km/h for a 90-km trip, and you only average 40 km/h for the first 40 km, what velocity must you average the rest of the way?

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Question 712312: If you must average 60 km/h for a 90-km trip, and you only average 40 km/h for the first 40 km, what velocity must you average the rest of the way?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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If you must average 60 km/h for a 90-km trip, and you only average 40 km/h for the first 40 km, what velocity must you average the rest of the way?
:
Find the time required for the trip:
90%2F60 = 1.5 hrs
:
Let s = velocity required for the last 50 km
:
40 km time + 50 km time = 1.5 hrs
40%2F40 + 50%2Fs = 1.5
1 + 50%2Fs = 1.5
subtract 1 from both sides
50%2Fs = .5
.5s = 50
s = 100 km/hr required for the last 50 km