Question 334470
Suppose you are traveling at an average of 55 miles per hour to your sisters house, and return at an average of 65 miles per hour. The total driving time is 12 hours. How far, in miles did you travel? 
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Let x = time (hours) it takes to travel to your sister's house
then
12-x = time (hours) it takes to return from your sister's house
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Distance to your sister's house: d = rt
55x
Distnace from your sister's house:
65(12-x)
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Since the distance is the same whether you're going to or returning from your sister's house, set both expressions (above) equal to each other and solve for x:
55x = 65(12-x)
55x = 780-65x
120x = 780
x = 6.5 hours (time to travel TO your sister's house)
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Distance then must be:
55x = 55(6.5) = 357.5 miles