Section: Mathematics
10)
A car averages 55 mph for the first 4 hours of a trip and averages 70 mph for each additional hour. The average speed for the entire trip was 60 mph. How many hours long is the trip?
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Explanation
Start with the equation
(55(4) + 70x) / 4+x = 60
= (220 + 70x) / 4+x = 60
Multiply both sides by 4+x
220 + 70x = 240 + 60x
Which gives you
10x = 20, so x = 2. Add this to the 4 hours and you have 6.
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