Difference between revisions of "2012 AIME I Problems/Problem 4"
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== Solution == | == Solution == | ||
| − | When they meet at the milepost, Sparky has been ridden for <math>n</math> miles total. Assume Butch rides Sparky for <math>a</math> miles, and Sundance rides for <math>n-a</math> miles. Thus, we can set up an equation, given that Sparky takes <math>\frac{1}{6}</math> hours per mile, Butch takes <math>\frac{1}{4}</math>, and Sundance takes <math>\frac{2}{5}</math>: <math>\frac{a}{6} + \frac{1}{4}(n-a) = \frac{n-a}{6} + \frac{2a}{5} \rightarrow a = \frac{5}{19}n </math> | + | When they meet at the milepost, Sparky has been ridden for <math>n</math> miles total. Assume Butch rides Sparky for <math>a</math> miles, and Sundance rides for <math>n-a</math> miles. Thus, we can set up an equation, given that Sparky takes <math>\frac{1}{6}</math> hours per mile, Butch takes <math>\frac{1}{4}</math>, and Sundance takes <math>\frac{2}{5}</math>: <math>\frac{a}{6} + \frac{1}{4}(n-a) = \frac{n-a}{6} + \frac{2a}{5} \rightarrow a = \frac{5}{19}n</math>. |
| − | + | Thus, the smallest possible value of <math>n</math> is <math>19</math>, and we plug in <math>n = 19</math> and <math>a = 5</math> to get <math>t = \frac{13}{3}</math> hours, or <math>260</math> minutes. Thus, our answer is <math>19 + 260 = \boxed{279}</math>. | |
== See also == | == See also == | ||
{{AIME box|year=2012|n=I|num-b=3|num-a=5}} | {{AIME box|year=2012|n=I|num-b=3|num-a=5}} | ||
Revision as of 11:02, 17 March 2012
Problem 4
Butch and Sundance need to get out of Dodge. To travel as quickly as possible, each alternates walking and riding their only horse, Sparky, as follows. Butch begins by walking while Sundance rides. When Sundance reaches the first of the hitching posts that are conveniently located at one-mile intervals along their route, he ties Sparky to the post and begins walking. When Butch reaches Sparky, he rides until he passes Sundance, then leaves Sparky at the next hitching post and resumes walking, and they continue in this manner. Sparky, Butch, and Sundance walk at 
and 
miles per hour, respectively. The first time Butch and Sundance meet at a milepost, they are 
miles from Dodge, and they have been traveling for 
minutes. Find 
.
Solution
When they meet at the milepost, Sparky has been ridden for miles total. Assume Butch rides Sparky for 
miles, and Sundance rides for 
miles. Thus, we can set up an equation, given that Sparky takes 
hours per mile, Butch takes 
, and Sundance takes 
: 
.
Thus, the smallest possible value of is 
, and we plug in 
and 
to get 
hours, or 
minutes. Thus, our answer is 
.
See also
| 2012 AIME I (Problems • Answer Key • Resources) | ||
| Preceded by Problem 3 |
Followed by Problem 5 | |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
| All AIME Problems and Solutions | ||
