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?
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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