Justin recently drove to visit his parents who live 96 miles away. On his way there his average speed was 20 miles per hour faster than on his way home (he ran into some bad weather). If Justin spent a total of 4 hours driving, find the two rates (in mph). Round your answer to two decimal places, if needed. Justin's average speed to his parents' house: mph

Justin's average speed from his parents' house: mph

Justin's average speed to his parents' house: x= 40mph

Justin's average speed from his parents' house: x+20=60 mph

Step-by-step explanation:

Let the average speed be x +20  

Then average speed from his parents' x

And the distance is S=96

Then we know :

Justin's average speed to his parents' house:  x= 40mph

Justin's average speed from his parents' house:  x+20=60 mph

Outward bound::

rate = x+9 ; dist = 100 m ; time = 100/(x+9) hrs

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Homeward

rate = x mph ; dist = 100 m ; time = 100/x hrs

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Equation:

time + time = 5 hrs

100/(x+9) + 100/x = 5 hrs

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100x + 100(x+9) = 5x(x+9)

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200x + 900 = 5x^2 + 45x

5x^2 - 155x - 900 = 0

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x^2 - 31x - 180 = 0

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x = 36 mph

x+9 = 45 mph

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so x=40km

and average speed=x+20=60mph

8121 because

130,000 divided by 16 is 8121