Difference between revisions of "2024 AMC 8 Problems/Problem 17"
Cellsecret (talk | contribs) (→Video Solution by CosineMethod [🔥Fast and Easy🔥]) |
m (→Problem) |
||
Line 2: | Line 2: | ||
A chess king is said to attack all the squares one step away from it, horizontally, vertically, or diagonally. For instance, a king on the center square of a <math>3</math> x <math>3</math> grid attacks all <math>8</math> other squares, as shown below. Suppose a white king and a black king are placed on different squares of a <math>3</math> x <math>3</math> grid so that they do not attack each other. In how many ways can this be done? | A chess king is said to attack all the squares one step away from it, horizontally, vertically, or diagonally. For instance, a king on the center square of a <math>3</math> x <math>3</math> grid attacks all <math>8</math> other squares, as shown below. Suppose a white king and a black king are placed on different squares of a <math>3</math> x <math>3</math> grid so that they do not attack each other. In how many ways can this be done? | ||
+ | |||
+ | <asy> | ||
+ | /* AMC8 P17 2024, revised by Teacher David */ | ||
+ | unitsize(29pt); | ||
+ | import math; | ||
+ | add(grid(3,3)); | ||
+ | |||
+ | pair [] a = {(0.5,0.5), (0.5, 1.5), (0.5, 2.5), (1.5, 2.5), (2.5,2.5), (2.5,1.5), (2.5,0.5), (1.5,0.5)}; | ||
+ | |||
+ | for (int i=0; i<a.length; ++i) { | ||
+ | pair x = (1.5,1.5) + 0.4*dir(225-45*i); | ||
+ | draw(x -- a[i], arrow=EndArrow()); | ||
+ | } | ||
+ | |||
+ | label("$K$", (1.5,1.5)); | ||
+ | </asy> | ||
<math>\textbf{(A)}\ 20 \qquad \textbf{(B)}\ 24 \qquad \textbf{(C)}\ 27 \qquad \textbf{(D)}\ 28 \qquad \textbf{(E)}\ 32</math> | <math>\textbf{(A)}\ 20 \qquad \textbf{(B)}\ 24 \qquad \textbf{(C)}\ 27 \qquad \textbf{(D)}\ 28 \qquad \textbf{(E)}\ 32</math> |
Revision as of 22:32, 8 February 2024
Contents
[hide]- 1 Problem
- 2 Solution 1
- 3 Solution 2
- 4 Video Solution 1 (super clear!) by Power Solve
- 5 Video Solution 2 by Math-X (First understand the problem!!!)
- 6 Video Solution 3 by OmegaLearn.org
- 7 Video Solution 4 by SpreadTheMathLove
- 8 Video Solution by NiuniuMaths (Easy to understand!)
- 9 Video Solution by CosineMethod [🔥Fast and Easy🔥]
- 10 Video Solution by Interstigation
- 11 See Also
Problem
A chess king is said to attack all the squares one step away from it, horizontally, vertically, or diagonally. For instance, a king on the center square of a x grid attacks all other squares, as shown below. Suppose a white king and a black king are placed on different squares of a x grid so that they do not attack each other. In how many ways can this be done?
Solution 1
Corners have spots to go and there are corners, so . Edges have spots to go and there are sides so, . That gives us spots to go into totally. So is the answer. ~andliu766
Solution 2
We see that the center is not a viable spot for either of the kings to be in, as it would attack all nearby squares.
This gives three combinations:
Corner-corner: There are 4 corners, and none of them are touching orthogonally or diagonally, so it's
Corner-edge: For each corner, there are two edges that don't border it,
Edge-edge: The only possible combinations of this that work are top-bottom and left-right edges, so for this type
Multiply by two to account for arrangements of colors to get ~ c_double_sharp
Video Solution 1 (super clear!) by Power Solve
Video Solution 2 by Math-X (First understand the problem!!!)
https://youtu.be/BaE00H2SHQM?si=Q2e8OfkuzKZXmoau&t=4624
~Math-X
Video Solution 3 by OmegaLearn.org
Video Solution 4 by SpreadTheMathLove
https://www.youtube.com/watch?v=Svibu3nKB7E
Video Solution by NiuniuMaths (Easy to understand!)
https://www.youtube.com/watch?v=V-xN8Njd_Lc
~NiuniuMaths
Video Solution by CosineMethod [🔥Fast and Easy🔥]
https://www.youtube.com/watch?v=quWFZIahQCg
Video Solution by Interstigation
https://youtu.be/ktzijuZtDas&t=1922
See Also
2024 AMC 8 (Problems • Answer Key • Resources) | ||
Preceded by Problem 16 |
Followed by Problem 18 | |
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.