<PRE><B>Question 177594</B>
Junior drove his rig on the Interstate 10 from San Antonio to El Paso. At the halfway point he noticed that he had been averaging 80mph, while his company requires his average speed to be 60mph. What must be his speed for the last half of the trip so that he will average 60mph for the entire trip.
The book also gives this hint: The distance from San Antonio to El Paso is irrelevant. Use D or simply make up a distance.
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1st half DATA:
distance = x miles ; rate = 80 mph; time = d/r = x/80 hrs
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Complete trip DATA:
distance = 2x miles ; rate = 60 mph; time = d/r = 2x/60 = x/30 hrs
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2nd half DATA:
distance = x miles ; 
time = total time - 1st half time = (x/30)-(x/80) = 50x/2400 = (1/48)x
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Therefore rate on the 2nd half = x/[(1/48)x] = 48 mph
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Cheers,
Stan H.</PRE>