SOLUTION: BOATING TRIP: Cesar starts out on a boating trip at 8 am. Cesar's boat can go 20 miles per hour in still water. How far downsream can Cesar go if the current is 5 miles per hour an

Question 515481: BOATING TRIP: Cesar starts out on a boating trip at 8 am. Cesar's boat can go 20 miles per hour in still water. How far downsream can Cesar go if the current is 5 miles per hour and he wishes to go down and back in 4 hours?
Answer by oberobic(2304) (Show Source): You can put this solution on YOUR website!
d = r*t is the basic distance equation.
.
r = 20 mph in still water
.
c = 5 mph is the current in the river
.
going upstream, the speed = r-c = 20-5 = 15
.
going downstream, the speed = r+c = 25
.
d = d each way (that is, he returns to the same point he started).
The roundtrip = 2d.
.
d/r = t
.
he wants to make the whole trip in 4 hr
.
d/15 + d/25 = 4 hr
.
(25d + 15d) / (15*25) = 4
.
cross multiply
.
40d = 4*15*25
.
d = 4*15*25/40
.
d = 75/2 = 37 1/2 miles
.
Always check your answer.
.
In this case, what can we check?
Time.
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37.5 miles/ 15 mph = 2.5 hr going upstream (against the current)
37.5 miles/ 25 mph = 1.5 hr going downstream (with the current)
2.5+1.5= 4 hr
Correct.
.
Done.
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