SOLUTION: Sally was able to drive an average of 16 miles per hour faster in her car after the traffic cleared. She drove 60 miles in traffic before it cleared and then drove another 92 miles

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Question 1125043: Sally was able to drive an average of 16 miles per hour faster in her car after the traffic cleared. She drove 60 miles in traffic before it cleared and then drove another 92 miles. If the total trip took 4 hours, then what was her average speed in traffic?
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39621) About Me  (Show Source):
You can put this solution on YOUR website!
                   SPEED        TIME            DISTANCE
Before Cleared       r           60/r            60
Traffic Clear       r+16         92/(r+16)       92
TOTAL                             4

60%2Fr%2B92%2F%28r%2B16%29=4

Answer by ikleyn(52824) About Me  (Show Source):
You can put this solution on YOUR website!
.
The "time" equation is


    60%2Fr + 92%2F%28r%2B16%29 = 4  hours


saying that the total time is the sum of the partial times.


You can reduce it to a quadratic equation and solve it.


But you also can use the "trial and error" method, which will quickly (in seconds) give you an


Answer.   r = 30 mph is the slow rate.

Even if it is not legal in your class to solve using this method, it will help you to use the factoring method while solving the quadratic equation.