SOLUTION: Jon recently drove to visit his parents who live 60 miles away. On his way there his average speed was 9 miles per hour faster than on his way home (he ran into some bad weather).
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Question 1149792: Jon recently drove to visit his parents who live 60 miles away. On his way there his average speed was 9 miles per hour faster than on his way home (he ran into some bad weather). If Jon spent a total of 3 hours driving, find the two rates. Answer by ikleyn(52794) (Show Source):
If x is the slower rate (in miles per hour), then the faster rate is (x+9) mph.
The "time" equation is
+ = 3 hours.
Simplify
+ = 1
then multiply both sides by x*(x+9)
20*(x+9) + 20x = x*(x+9)
20x + 180 + 20x = x^2 + 9x
x^2 - 31x - 180 = 0
= = = .
Only positive root makes sense x = = 36.
Answer. The slower rate is 36 mph; the faster rate is 36+9 = 45 mph.
Solved.
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Using "time" equation is the STANDARD method of solving such problems.
From this lesson, learn on how to write, how to use and how to solve a "time" equation.
