SOLUTION: I am having a hard time figuring this word problem out. Can you please help. Upstream, downstream. Junior’s boat will go 15 miles per hour in still water. If he can go 12 miles d

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: I am having a hard time figuring this word problem out. Can you please help. Upstream, downstream. Junior’s boat will go 15 miles per hour in still water. If he can go 12 miles d      Log On


   

Question 335696: I am having a hard time figuring this word problem out. Can you please help.
Upstream, downstream. Junior’s boat will go 15 miles per
hour in still water. If he can go 12 miles downstream in the
same amount of time as it takes to go 9 miles upstream,
then what is the speed of the current?
Found 2 solutions by Fombitz, stanbon:
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Rate*Time=Distance
.
.
.
Let's call the speed of the current C.
When you go downstream, you add the speed of the boat and the current,
1.%2815%2BC%29t=12
When you go upstream, you subtract the current from the boat speed,
2.%2815-C%29t=9
From eq. 1,
t=12%2F%2815%2BC%29
Substitute into eq. 2,
%2815-C%29%2A%2812%2F%2815%2BC%29%29=9
12%2815-C%29=9%2815%2BC%29
180-12C=135%2B9C
-21C=-45
C=45%2F21=15%2F7 mph

Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Junior’s boat will go 15 miles per hour in still water.
If he can go 12 miles downstream in the
same amount of time as it takes to go 9 miles upstream,
then what is the speed of the current?
---
Downstream DATA:
distance = 12 miles ; rate = 15+c mph ; time = d/r = 12/(15+c) hrs
--------------------
Upstream DATA:
distance = 9 miles ; rate = 15-c mph ; time = d/r = 9/(15-c) hrs
--------------------
Equation:
time up = time down
8/(15-c) = 12/(15+c)
9(15+c) = 12(15-c)
9*15+9c = 12*15-12c
21c = 3(15)
c = (1/7)15
c = 2.5 mph (speed of the current)
=======================================
Cheers,
Stan H.
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