Respuesta :
Answer: The speed of the current is 3 miles per hour.
The speed of the boat in still water is 10 miles per hour
Step-by-step explanation:
Let the speed of the boat be x miles per hour
Let the speed of the current be y miles per hour
Speed = distance / time
If the boat moves 39 miles downstream in 3 hours, then, the speed is
39/3= 13 miles per hour
Let us assume that it moved it moved in the same direction with the current hence, it moved in still water
The total speed would be x + y. Therefore
x + y = 13 - - - - - - -1
If the boat moves 21 miles upstream in 3 hours, the the speed is
21/ 3 = 7 miles per hour
It is assumed that it moved in the opposite direction to the current.
The total speed would be x - y. Therefore
x - y = 7 - - - - - - -2
Adding equation 1 and equation 2, it becomes
2x = 20
x = 20/2 = 10 miles per hour
y = 13 - x
y = 13 - 10 = 3 miles per hour
