SOLUTION: Please help, I'm stumped!!! A hydrofoil stops for equal amounts of time at three ports between Southport and Martintown, which are 30 km apart. The hydrofoil is actually under w

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Question 785369: Please help, I'm stumped!!!
A hydrofoil stops for equal amounts of time at three ports between Southport and Martintown, which are 30 km apart. The hydrofoil is actually under way for 15 min of the trip. At most how long can the hydrofoil remain at each port if the average speed for the trip, including stops, is to be at least 50 km/h?
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
x= time stopped at each port (in minutes)
3x= total time stopped at one or another port (in minutes)
The hydrofoil is moving for only 15 minutes of the trip (stopped for the rest of the trip time).
3x%2B15= total trip time (in minutes)
%283x%2B15%29%2F60=3x%2F60%2B15%2F60=0.05x%2B0.25= total trip time (in hours)
The average speed is the total distance divided by the total time
%2250+km%2Fh%22=30km%2F%280.05x%2B0.25%29h-->0.05x%2B0.25=30%2F50-->0.05x%2B0.25=0.60-->0.05x=0.60-0.25--> 0.05x=0.35-->x=0.35%2F0.05--> highlight%28x=7%29