SOLUTION: I am not sure how to set this equation up? I am really getting frustrated and all I need help with is understanding how to use the D=r(t) table to set this up. Here is the question
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Question 359035: I am not sure how to set this equation up? I am really getting frustrated and all I need help with is understanding how to use the D=r(t) table to set this up. Here is the question:
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?
Here is what I have so far:
D R T
12mile 15mph = 3/5 hr
9miles 15mph = 4/5 hr
Is this correct or am I making an error somewhere is setting this up? Found 2 solutions by mananth, ewatrrr:Answer by mananth(16946) (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?
...
current speed =xmph
downstream speed = x+15
upstream speed = 15-x
..
downstream distance = 12 miles
time downstream = 12/x+15
..
upstream distance = 9 miles
upstream time = 9/15-x
..
these times are same
12/(x+15)=9/(15-x)
12(15-x)=9(x+15)
180-12x=9x+135
-12x-9x=135-180
-21x=-45
/-21
x=45/21
x= 2.14 mph speed of current
m.ananth@hotmail.ca
Hi,
distance formula: d = rt t = d/r
Letting c be the rate of the current
12 miles downstream in the 'same amount of time' as it takes to go 9 miles upstream
Cross multiplying to solve for c
12(15 -c ) = 9(15+c)
12*15mph - 9*15mph = 2c
45 = 2c
22.5mph= c
