Answer: The speed of Ina in still water is 5mph
Explanation:
If the speed of Ina on still water is x, and the speed of the river is y:
The total speed of Ina when she goes along with the current is:
S = x + y
when she goes against the current we have:
St = x - y.
Now we can use the relation:
speed = time/velocity.
along with the current, we have:
x + y = 12mi/2h = 6mi/h
against the current we have:
x - y = 12mi/3h = 4mi/h
So we have the equations
x + y = 6mi/h
x - y = 4mi/h
in the first equation we can isolate x
x = 6mi/h - y
now we replace this in the second equation:
(6mi/h - y) - y = 4mi/h
6mi/h - 2y = 4mi/h
-2*y = 4mi/h - 6mi/h = -2mi/h
y = 1mi/h
now we replace this in the first equation:
x + 1mi/h = 6mi/h
x = 5mi/h.
The speed of Ina in still water is 5mph