SOLUTION: Max runs the first km of her training session at 8km/h. At least how many kilometers must she run at 15 km/h in order to average 12km/h for the whole session?
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Question 100921: Max runs the first km of her training session at 8km/h. At least how many kilometers must she run at 15 km/h in order to average 12km/h for the whole session? Answer by ankor@dixie-net.com(22740) (Show Source):
You can put this solution on YOUR website! Max runs the first km of her training session at 8km/h. At least how many kilometers must she run at 15 km/h in order to average 12km/h for the whole session
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Time = distance/speed
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Let d = distance required at 15 km/h to average 12km/h
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Write a time equation
Time at 8 km/h + time at 15 km/h = time at 12/km/h + =
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Multiply equation by 120 to get rid of the denominators
120* + 120* = 120*
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Cancel out the denominators:
15(1) + 8(d) = 10(d+1)
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15 + 8d = 10d + 10
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8d - 10d = 10 - 15
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-2d = -5
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d = + 5/2 or 2.5 km at 15 km/hr rate
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Total distance would be 3.5 km
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Check solution by calculating av speed = dist/time
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Find the time: + = + = + = 7/24 hr, is the total time
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Check average speed (dist/time)
7/2 (3.5) divided by 7/24 * = 24/2 = 12 km/hr
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Sorry, I got twisted around on the first attempt
