Answer: The speed of the boat in still water is 6.5 mph.
The speed of the current is 2.5 mph
Step-by-step explanation:
Let x represent the speed of the boat in still water.
Let y represent the speed of the current.
A boat going upstream on The River averages 4 mph. Assuming it travelled against the current while going upstream, its total speed would be (x - y) mph. It means that
x - y = 4- - - - - - - - - - - -1
Going downstream, the boat averages 9 mph. Assuming it travelled with the current while going upstream, its total speed would be (x + y) mph. It means that
x + y = 9- - - - - - - - - - - -2
Adding both equations, it becomes
2x = 13
x = 13/2
x = 6.5 mph
Substituting x = 6.5 into equation 1, it becomes
6.5 - y = 4
y = 6.5 - 4
y = 2.5 mph
