Difference between revisions of "2018 AIME II Problems/Problem 1"
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Points <math>A</math>, <math>B</math>, and <math>C</math> lie in that order along a straight path where the distance from <math>A</math> to <math>C</math> is <math>1800</math> meters. Ina runs twice as fast as Eve, and Paul runs twice as fast as Ina. The three runners start running at the same time with Ina starting at <math>A</math> and running toward <math>C</math>, Paul starting at <math>B</math> and running toward <math>C</math>, and Eve starting at <math>C</math> and running toward <math>A</math>. When Paul meets Eve, he turns around and runs toward <math>A</math>. Paul and Ina both arrive at <math>B</math> at the same time. Find the number of meters from <math>A</math> to <math>B</math>. | Points <math>A</math>, <math>B</math>, and <math>C</math> lie in that order along a straight path where the distance from <math>A</math> to <math>C</math> is <math>1800</math> meters. Ina runs twice as fast as Eve, and Paul runs twice as fast as Ina. The three runners start running at the same time with Ina starting at <math>A</math> and running toward <math>C</math>, Paul starting at <math>B</math> and running toward <math>C</math>, and Eve starting at <math>C</math> and running toward <math>A</math>. When Paul meets Eve, he turns around and runs toward <math>A</math>. Paul and Ina both arrive at <math>B</math> at the same time. Find the number of meters from <math>A</math> to <math>B</math>. | ||
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+ | ==Solution== | ||
+ | We know that in the same amount of time given, Ina will run twice the distance of Eve, and Paul would run quadruple the distance of Eve. Let's consider the time it takes for Paul to meet Eve: Paul would've run 4 times the distance of Eve, which we can denote as <math>d</math>. Thus, the distance between <math>B</math> and <math>C</math> is <math>4d+d=5d</math>. In that given time, Ina would've run twice the distance <math>d</math>, or <math>2d</math> units. | ||
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+ | Now, when Paul starts running back towards <math>A</math>, the same amount of time would pass since he will meet Ina at his starting point. Thus, we know that he travels another <math>4d</math> units and Ina travels another <math>2d</math> units. | ||
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+ | Therefore, drawing out the diagram, we find that <math>2d+2d+4d+d=9d=1800 \implies d=200</math>, and distance between <math>A</math> and <math>B</math> is the distance Ina traveled, or <math>4d=4(200)=\boxed{800}</math> | ||
{{AIME box|year=2018|n=II|before=First Problem|num-a=2}} | {{AIME box|year=2018|n=II|before=First Problem|num-a=2}} | ||
{{MAA Notice}} | {{MAA Notice}} |
Revision as of 10:06, 24 March 2018
Problem
Points ,
, and
lie in that order along a straight path where the distance from
to
is
meters. Ina runs twice as fast as Eve, and Paul runs twice as fast as Ina. The three runners start running at the same time with Ina starting at
and running toward
, Paul starting at
and running toward
, and Eve starting at
and running toward
. When Paul meets Eve, he turns around and runs toward
. Paul and Ina both arrive at
at the same time. Find the number of meters from
to
.
Solution
We know that in the same amount of time given, Ina will run twice the distance of Eve, and Paul would run quadruple the distance of Eve. Let's consider the time it takes for Paul to meet Eve: Paul would've run 4 times the distance of Eve, which we can denote as . Thus, the distance between
and
is
. In that given time, Ina would've run twice the distance
, or
units.
Now, when Paul starts running back towards , the same amount of time would pass since he will meet Ina at his starting point. Thus, we know that he travels another
units and Ina travels another
units.
Therefore, drawing out the diagram, we find that , and distance between
and
is the distance Ina traveled, or
2018 AIME II (Problems • Answer Key • Resources) | ||
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