Question 1131896: A jogger runs into the country side at a rate of 10mph. He returns along the same route at 6mph. If the total trip took 1 hour, 36 minutes, how far did he jog?
Found 3 solutions by greenestamps, josgarithmetic, Alan3354:
Answer by greenestamps(13195)   (Show Source):
You can put this solution on YOUR website!
The ratio of the two speeds is 10:6, or 5:3. Since the distances are the same, the ratio of times is then 3:5. So he spent 3/8 of the time on the trip going out and 5/8 of the time returning.
The total time is 1 hour 36 minutes, or 1 3/5 hours, or 8/5 hours.
His time returning was then 5/8 of 8/5 hours, or 1 hour.
His rate returning was 6mph; 6mph for 1 hour makes the return trip 6 miles.
So the total jog was 12 miles.
Answer by josgarithmetic(39614)  (Show Source):
Answer by Alan3354(69443)  (Show Source):
You can put this solution on YOUR website! A jogger runs into the country side at a rate of 10mph. He returns along the same route at 6mph. If the total trip took 1 hour, 36 minutes, how far did he jog?
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The formula for round-trip speed is similar to parallel work and parallel resistance.
---RT Avg = 2*r1*r2/(r1+r2)
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Avg = 2*10*6/(10+6) = 120/16 = 7.5 mi/hr
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The RT distance = r*t = 7.5 mi/hr * 1.6 hours = 12 miles round trip
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I'm not a proponent of memorizing a lot of formulas, but this one, and parallel work, parallel resistance, etc, are useful.
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PS Notice that the avg RT speed does not vary with the distance. This was an important factor in the Michelson-Morley experiment that disproved the existence of the "ether."
Ether was put on the shelf with phlogiston.
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