let r=rowing speed
c=current speed
1=distance
Speed for rowing upstream is (r-c) as u have to row against the water current
Speed for rowing downstream is (r+c) as u row along the current
Speed for rowing in still water will be just r
Time taken for rowing upstream is 84 min
1=(r-c)*84
Let t=downstream time
1=(r+c)*t
Question says that they can row the same course down stream in 9 minutes less than they can row it in still water
So time taken for rowing in still water will be (t+9)
1=r*(t+9)
Restating above 3 questions as
r-c = 1/84
r+c = 1/t
r = 1/(t+9)
Adding statements 1 & 2 gives
2r = 1/84 + 1/t
Substituting r = 1/(t+9) in above
2/(t+9) = 1/84 + 1/t
Rearranging terms will form
t^2-75t+756=0
By solving, t= 12 or 63
Kudos please if helped
riankita wrote:
gracie wrote:
ramkryp wrote:
A crew can row a certain course up the stream in 84 minutes; they can row the same course down stream in 9 minutes less than they can row it in still water. How long would they take to row down with the stream
A. 45 or 23 minutes
B. 63 or 12 minutes
C. 60 minutes
D. 19 minutes
E. 25 minutes
let r=rowing speed
c=current speed
t=downstream time
1=distance
r+c=1/t
r-c=1/84
adding, 2r=1/t+1/84
r=1/(t+9)
thus, (1/t+1/84)/2=1/(t+9)
➡t^2-75t+756=0
(t-63)(t-12)=0
t=63 or 12 minutes
B
Could someone explain the process again?
Thanks
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