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The speed downstream is = 24 km/h.
It is equal to the sum of the boat speed at still water (U) and the current speed (v):
u + v = 24. (1)
The speed downstream is = 20 km/h.
It is equal to the DIFFERENCE of the boat speed at still water (U) and the current speed (v):
u - v = 20. (2)
Thus you have these two equations for 2 unknowns:
u + v = 24, (1)
u - v = 20. (2)
Add the equations. You will get
2u = 24 + 18 = 44 ====> u = = 22.
Thus you just found the speed of the the boat in still water. It is 22 km/h.
Then from (1) v = 24-u = 24 - 22 = 2 km/h.
Answer. The speed of the the boat in still water is 22 km/h.
The speed of the current is 2 km/h.
Solved.
To see other similar solved problems, look into the lessons
- Wind and Current problems
- More problems on upstream and downstream round trips
- Wind and Current problems solvable by quadratic equations
- Unpowered raft floating downstream along a river
- Selected problems from the archive on the boat floating Upstream and Downstream
- Selected problems from the archive on a plane flying with and against the wind
in this site.