SOLUTION: a bus driver wants to average at least 40 mph on a 70-mi trip. if the first 35 mi take the driver 1 hr, what should be the lowest average speed for the second 35 mi?

Question 606716: a bus driver wants to average at least 40 mph on a 70-mi trip. if the first 35 mi take the driver 1 hr, what should be the lowest average speed for the second 35 mi?

Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
a bus driver wants to average at least 40 mph on a 70-mi trip. if the first 35 mi take the driver 1 hr, what should be the lowest average speed for the second 35 mi?
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For a round-trip, or with parts of equal length, the avg speed is
Avg = 2*r1*r2/(r1 + r2)
40 = 2*35*r2/(35 + r2)
1400 + 40r2 = 70r2
r2 = 1400/30 mi/hr
140/3 mi/hr
=~ 46.67 mi/hr
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