Question 292561
going she travels at 40 miles per hour. 
returning, travels at 90 miles per hour. 
What is Beatriz’s average commute velocity?
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Let d = distance traveled one way
Let s = average speed for the commute
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Write time equation: Time = dist/speed
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Go time + return time = total time
{{{d/40}}} + {{{d/90}}} = {{{(2d)/s}}}
multiply equation by 360s. results:
9ds + 4ds = 360(2d)
13ds = 720d
Divide both sides by d
13s = 720
s = {{{720/13}}}
s = 55.38 mph is the average speed
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