The speed of the current in a river is 6 mph. A ferry operator who works that part of the river is looking to buy a new boat for his business. Every day, his route takes him 22.5 miles against the current and back to his dock, and he needs to make this trip in a total of 9 hours. He has a boat in mind, but he can only test it on a lake where there is no current. How fast must the boat go on the lake in order for it to serve the ferry operator’s needs?
@amistre64 @Mertsj @e.mccormick @zepdrix @agent0smith help i dont understand?

Question

The speed of the current in a river is 6 mph. A ferry operator who works that part of the river is looking to buy a new boat for his business. Every day, his route takes him 22.5 miles against the current and back to his dock, and he needs to make this trip in a total of 9 hours. He has a boat in mind, but he can only test it on a lake where there is no current. How fast must the boat go on the lake in order for it to serve the ferry operator’s needs?
@amistre64 @Mertsj @e.mccormick @zepdrix @agent0smith  help i dont understand?

mertsj · Answer

The problem is asking you to find the speed of the boat in still water.  Do you understand that part?

anonymous · Answer

Yes

mertsj · Answer

Let r = the speed of the boat in still water.
When the boat is going with the current, its speed is r+6
When the boat is going against the current, its speed is r-6

mertsj · Answer

Let's say it takes him t hours to go the 22.5 miles with the current.
Then , since rt = d, we have t(r+6)=22.5

mertsj · Answer

Then to go the 22.5 miles against the current will take him the rest of the 9 hours which is 9-t and so we have:
(r-6)(9-t)=22.5

mertsj · Answer

Solve that system.

anonymous · Answer

so you want me to solve (r-6)(9-t)=22.5?