SOLUTION: I am confused about this question. In the book it says that the average is not 50 miles per hour. I need to know how to set up the problem to solve it: Joan Bidney travels from C

Question 179315This question is from textbook Merrill Algebra 1
: I am confused about this question. In the book it says that the average is not 50 miles per hour. I need to know how to set up the problem to solve it:
Joan Bidney travels from Cincinnati to Winston-Salem at an average rate of 40 miles per hour and returns at an average rate of 60 miles per hour. What is her average speed for the trip? (Hint: the average speed is not 50 miles per hour.) This question is from textbook Merrill Algebra 1

Answer by Mathtut(3670) (Show Source): You can put this solution on YOUR website!
ok, lets call the distance d, the rate r, and the time t
:
d=40t.....trip to
d=60t.....trip back
:
solve for t
:
t=d/40....trip to
t=d/60....trip back
:
now lets take the time traveled for the entire to and back trip and multiply it by average rate for the whole trip which will be equal to 2d
:

:
found common denominator on left
:
divided all terms by d
:
combined numerator on left and multiplied by 120 on both sides
:
mph average for whole trip
:
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