Difference between revisions of "2024 AMC 8 Problems/Problem 23"
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− | Let <math>f(x, y)</math> be the number of cells the line segment from <math>(0, 0)</math> to <math>(x, y)</math> passes through. The problem is then equivalent to finding <cmath>f(5000-2000, 8000-3000)=f(3000, 5000).</cmath> Sometimes the segment passes through lattice points in between the endpoints, which happens <math>\text{gcd}(3000, 5000)-1=999</math> times. This partitions the segment into <math>1000</math> congruent pieces that pass through <math>f(3, 5)</math> cells, which means the answer is <cmath>1000f(3, 5).</cmath> Note that a new square is entered when the lines pass through one of the lines in the coordinate grid, which for <math>f(3, 5)</math> happens <math>3-1+5-1=6</math> times. Because <math>3</math> and <math>5</math> are relatively prime, no lattice point except for the endpoints intersects the line segment from <math>(0, 0)</math> to <math>(3, 5).</math> This means that including the first cell closest to <math>(0, 0),</math> The segment passes through <math>f(3, 5)=6+1=7</math> cells. Thus, the answer is <math>\boxed{7000}.</math> Alternatively, <math>f(3, 5)</math> can be found by drawing an accurate diagram, leaving you with the same answer. | + | Let <math>f(x, y)</math> be the number of cells the line segment from <math>(0, 0)</math> to <math>(x, y)</math> passes through. The problem is then equivalent to finding <cmath>f(5000-2000, 8000-3000)=f(3000, 5000).</cmath> Sometimes the segment passes through lattice points in between the endpoints, which happens <math>\text{gcd}(3000, 5000)-1=999</math> times. This partitions the segment into <math>1000</math> congruent pieces that each pass through <math>f(3, 5)</math> cells, which means the answer is <cmath>1000f(3, 5).</cmath> Note that a new square is entered when the lines pass through one of the lines in the coordinate grid, which for <math>f(3, 5)</math> happens <math>3-1+5-1=6</math> times. Because <math>3</math> and <math>5</math> are relatively prime, no lattice point except for the endpoints intersects the line segment from <math>(0, 0)</math> to <math>(3, 5).</math> This means that including the first cell closest to <math>(0, 0),</math> The segment passes through <math>f(3, 5)=6+1=7</math> cells. Thus, the answer is <math>\boxed{7000}.</math> Alternatively, <math>f(3, 5)</math> can be found by drawing an accurate diagram, leaving you with the same answer. |
~BS2012 | ~BS2012 |
Revision as of 22:06, 26 January 2024
Contents
Problem
Rodrigo has a very large sheet of graph paper. First he draws a line segment connecting point to point
and colors the
cells whose interiors intersect the segment, as shown below. Next Rodrigo draws a line segment connecting point
to point
. How many cells will he color this time?
Solution 1
Let be the number of cells the line segment from
to
passes through. The problem is then equivalent to finding
Sometimes the segment passes through lattice points in between the endpoints, which happens
times. This partitions the segment into
congruent pieces that each pass through
cells, which means the answer is
Note that a new square is entered when the lines pass through one of the lines in the coordinate grid, which for
happens
times. Because
and
are relatively prime, no lattice point except for the endpoints intersects the line segment from
to
This means that including the first cell closest to
The segment passes through
cells. Thus, the answer is
Alternatively,
can be found by drawing an accurate diagram, leaving you with the same answer.
~BS2012
Note: A general form for finding is
We subtract
to account for overlapping, when the line segment goes through a lattice point.
~mathkiddus
Video Solution by Power Solve (crystal clear!)
https://www.youtube.com/watch?v=fzgWcEz4K_A
Video Solution 1 by Math-X (First fully understand the problem!!!)
https://www.youtube.com/watch?v=dqqAk-Cd_5M
~Math-X
Video Solution 2 by OmegaLearn.org
Video Solution by SpreadTheMathLove
https://www.youtube.com/watch?v=x8Zo7QOB-us
Video Solution by CosineMethod [🔥Fast and Easy🔥]
https://www.youtube.com/watch?v=w8zha2ijVQQ
See Also
2024 AMC 8 (Problems • Answer Key • Resources) | ||
Preceded by Problem 22 |
Followed by Problem 24 | |
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 AJHSME/AMC 8 Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.