SOLUTION: The speed of a stream is 4mph. If a boat travels 80 miles downstream in the same time that it takes to travel 40 miles upstream, what is the speed of the boat in still water?

Question 161390: The speed of a stream is 4mph. If a boat travels 80 miles downstream in the same time that it takes to travel 40 miles upstream, what is the speed of the boat in still water?
Answer by checkley77(12844) (Show Source): You can put this solution on YOUR website!
D=RT
80=(D+4)T
40=(D-4)T
SEEING AS THE TIMES ARE THE SAME WE HAVE:
80/(D+4)=40/(D-4)
80(D-4)=40(D+4)
80D-320=40D+160
80D-40D=160+320
40D=480
D=480/40
D=12 MPH FOR THE CURRENT.
PROOF;
80/(12+4)=40/(12-4)
80/16=40/8
16*40=80*8
640=640
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Hi Thank you for your time. One that I simply cannot get is: An airplane
travels 600 miles against the wind in 4 hrs. and makes the return trip with the
same wind in 2 hrs. Find the rate of the wind. The answer is either: 75, 150,
225, or 300mph. I can't seem to get the formula and it is driving me crazy!
Can you help?
D=R*T
600=R*4
R=600/4=150 MPH AGAINST THE WIND.
600=R*2
R=600/2=300 MPH WITH THE WIND.
(300-150)/2=150/2=75 MPH IS THE SPEED OF THE WIND.
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