Question 881295
What is your average rate if you drive to campus averaging 50 mph and return home on the same route averaging 40 mpg
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It's not 45, the avg of 50 & 40 because more time is spent going 40.
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There's a formula similar to parallel resistance and parallel flows 

Avg = 2*50*40/(50 + 40) = 4000/90 = 400/9
= 44.444... mi/hr (not mpg)
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I can derive the formula if you like.