SOLUTION: roselinda rode her bike for 60 miles at 30 miles per hour and then rode 20 miles at 10 miles per hour. how fast would she have to ride for the next 20 miles to have an overall aver

Question 704483: roselinda rode her bike for 60 miles at 30 miles per hour and then rode 20 miles at 10 miles per hour. how fast would she have to ride for the next 20 miles to have an overall average speed of 20 miles per hour for the entire trip?
Found 2 solutions by stanbon, lwsshak3:
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
roselinda rode her bike for 60 miles at 30 miles per hour and then rode 20 miles at 10 miles per hour. how fast would she have to ride for the next 20 miles to have an overall average speed of 20 miles per hour for the entire trip?
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1st leg time: 60/30 = 2 hrs
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2nd leg time: 20/10 = 2 hrs
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3rd leg DATA: distance = 20 miles ; rate = x mph ; time = 20/x hrs
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Overall Average Speed = (overall distance)/(overall time)
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Equation:
(60 + 20 + 20)/(2 + 2 + 20/x) = 20 mph
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100/(4 + 20/x) = 20
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Cross-multiply:
100 = 80 + 400/x
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20 = 400/x
x = 20 mph (speed on the 3rd link)
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Cheers,
Stan H.
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
roselinda rode her bike for 60 miles at 30 miles per hour and then rode 20 miles at 10 miles per hour. how fast would she have to ride for the next 20 miles to have an overall average speed of 20 miles per hour for the entire trip?
**
let x=speed required for an overall average speed of 20 mph
Speed=distance/travel time
Total distance=60+20+20=100 miles
Total travel time=60/30+20/10+20/x=2+2+20/x=4+20/x=(4x+20)/x
distance/travel time=100/(4x+20)/x=20
100x/(4x+20)=20
80x+400=100x
20x=400
x=20
speed required for an overall average speed of 20 mph=20 mph
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