SOLUTION: It took 4.5 hours to drive to her mother's house. On her trip on Sunday , it took 5 hours. Her average speed on Sunday was 4mph slower than on Saturday. What was her average spe

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Question 266541: It took 4.5 hours to drive to her mother's house. On her trip on Sunday , it took 5 hours. Her average speed on Sunday was 4mph slower than on Saturday. What was her average speed on Sunday?
Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
This is an RTD problem. Here is a table based on the above information:
driving . . . . rate . . . . time . . . . distance
Sat . . . . . . . . r . . . . . .(4.5) . . . . . . 4.5r
Sun . . . . . . . r - 4 . . . . 5 . . . . . . . . 5r - 20
total . . . . . . . . . . . . . . .9.5 . . . . . . 9.5r - 20
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Looking at the third column, we get
4.5r = 5r - 20
subtract 5r to get
-.5r = -20
r= 40
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her average speed Saturday was 40
her average speed Sunday was 36