<PRE><B>Question 556337</B>
A car travels one lap around a 1 mile track at an average speed of 30 miles per hour. At what average speed must the car travel on the second lap so that the average speed for both laps is 50 miles per hour.
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2 mi at 50 mi/hr takes 1/25 hr
1 mi at 30 mi/hr takes 1/30 hr
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He has to go 1 mile in (1/25 - 1/30) hr = 1/150 hr
His speed needed is 150 mi/hr
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Check:
Avg speed for a round trip, or of 2 equal distances is
2*30*150/(30 + 150) = 9000/180
= 50 mi/hr
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