Difference between revisions of "2007 AMC 12B Problems/Problem 13"
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Revision as of 23:31, 10 April 2013
Problem 13
A traffic light runs repeatedly through the following cycle: green for seconds, then yellow for
seconds, and then red for
seconds. Leah picks a random three-second time interval to watch the light. What is the probability that the color changes while she is watching?
Solution
The traffic light runs through a second cycle.
Letting reference the moment it turns green, the light changes at three different times:
,
, and
This means that the light will change if the beginning of Leah's interval lies in
,
or
This gives a total of seconds out of
See Also
2007 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 12 |
Followed by Problem 14 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
All AMC 12 Problems and Solutions |