SOLUTION: 1) On a recent trip, Sarah's car traveled 20 mph faster on the first 200 miles than it did on the remaining 80 miles. The total time for the trip was 4 hours. Find the speed of Sar
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-> SOLUTION: 1) On a recent trip, Sarah's car traveled 20 mph faster on the first 200 miles than it did on the remaining 80 miles. The total time for the trip was 4 hours. Find the speed of Sar
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Question 365402: 1) On a recent trip, Sarah's car traveled 20 mph faster on the first 200 miles than it did on the remaining 80 miles. The total time for the trip was 4 hours. Find the speed of Sarah's car on the first part of the tip.
2)A boat ride takes 8 hours to travel 80 miles upstream and 5 hours to return to its starting point. Find the speed of the boat in still water and the speed of the current.
I simply don't understand how to get these answers with the formula d=rt. Not all of the information is present. Answer by mananth(16946) (Show Source):
You can put this solution on YOUR website! 1) On a recent trip, Sarah's car traveled 20 mph faster on the first 200 miles than it did on the remaining 80 miles. The total time for the trip was 4 hours. Find the speed of Sarah's car on the first part of the trip.
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80 miles ------------- x mph
200 miles ------------ x+20 mph
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Time for first part = 200/(x+20)
Time for second part = 80/x
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time for first part + time for second part = 4 hours
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200/(x+20) + 80/x = 4
LCD = x(x+20)
(200x+80(x+20))/x(x+20)=4
(200x+80x+1600)=4x(x+20)
280x+1600= 4x^2+80x
4x^2+80x-280x-1600=0
4x^2-200x-1600=0
/4
x^2-50x-400=0
discriminant = 4100
x1= (50+sqrt(4100))/2
x1= 57.10 mph---- second part speed
x2 will be negative so ignore.
First part speed = 57.10 + 20 = 77.01 mph
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2)A boat ride takes 8 hours to travel 80 miles upstream and 5 hours to return to its starting point. Find the speed of the boat in still water and the speed of the current.
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let speed of boat in still water = x mph
speed of current = y mph
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Upstream
80 miles 8 hours
speed = 10 mph
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downstream
80 miles ---- 5 hours
speed = 16 mph
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x+y=16
x-y = 8
add the two equations
2x=24
/2
x= 12 mph speed of boat in still water
y= 4 mph speed of current
...
m.ananth@hotmail.ca
