SOLUTION: You drive home at an average speed of 30mph to get a take-out pizza in town. You drive back home on same route at an average speed of 60mph(you want to get home before the pizza co

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Question 113722: You drive home at an average speed of 30mph to get a take-out pizza in town. You drive back home on same route at an average speed of 60mph(you want to get home before the pizza cools off). What is your average speed for the entire round trip?
*(Hint: It is NOT 45mph, as your intuition might suggest.)
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
You drive home at an average speed of 30mph to get a take-out pizza in town. You drive back home on same route at an average speed of 60mph(you want to get home before the pizza cools off). What is your average speed for the entire round trip?
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To pizza DATA:
rate = 30 mph ; distance = x miles ; time = d/r=x/30 hrs
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To home DATA:
rate = 60 mph ; distance = x miles ; time = d/r = x/60 hrs
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Average speed = distance / time = 2x/[x/30 + x/60]
= 2x / [90x/1800]
= 2x / [x/20]
= 40 mph
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Cheers,
Stan H.