Question 209211: Julie and Eric row their boat (at a constant speed) 45 miles downstream for 5 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 9 hours. Find the rate of the current.
Found 2 solutions by nerdybill, MathTherapy:
Answer by nerdybill(7384)   (Show Source):
You can put this solution on YOUR website! Julie and Eric row their boat (at a constant speed) 45 miles downstream for 5 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 9 hours. Find the rate of the current.
.
You will need to apply the "distance formula":
d = rt
where
d is distance
r is rate or speed
t is time
.
Let x = rate of the current
and y = rate Julie and Eric can row
.
Since we have two variables, we'll need two equations:
Downstream:
5(y+x) = 45 (equation 1)
Upstream:
9(y-x) = 45 (equation 2)
.
Solve equation 2 for y:
9(y-x) = 45
y-x = 5
y = 5+x
.
Substitute the above into equation 1 and solve for x:
5(y+x) = 45
5(5+x+x) = 45
5+x+x = 9
2x = 4
x = 2 mph (rate of the current)
Answer by MathTherapy(10551)  (Show Source):
You can put this solution on YOUR website! Julie and Eric row their boat (at a constant speed) 45 miles downstream for 5 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 9 hours. Find the rate of the current.
The speed that they travelled at, downstream, with the current = 9 mph (45/5)
The speed that they travelled at, upstream, against the current = 5 mph (45/9)
Let the rate of the current be C
Then we'll have: Downstream speed - current = Upstream speed + current, or,
9 - C = 5 + C
- 2C = - 4
Therefore, the speed of the current is:  mph.
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