2023 AMC 8 Problems/Problem 23
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[hide]Problem
Each square in a grid is randomly filled with one of the gray and white tiles shown below on the right. What is the probability that the tiling will contain a large gray diamond in one of the smaller grids? Below is an example of such tiling.
Solution 1
Probability is total favorable outcomes over total outcomes, so we can find these separately to determine the answer.
There are ways to choose the big diamond location from our square grid. From our given problem there are different arrangements of triangles for every square. This implies that from having diamond we are going to have distinct patterns outside of the diamond. This gives a total of favorable cases.
There are 9 squares and 4 possible designs for each square, giving total outcomes. Thus, our desired probability is .
-apex304 and TaeKim
Solution 2 (Linearity of Expectation)
Let , and denote the smaller squares within the square in some order. For each , let if it contains a large gray diamond tiling and otherwise. This means that is the probability that square has a large gray diamond, so is our desired probability. However, since there is only one possible way to arrange the squares within every square to form such a tiling, we have for all (as each of the smallest tiles has possible arrangements), and from the linearity of expectation we get ~eibc
Remark: This method might be too advanced for the AMC 8, and is probably unnecessary (refer to the other solutions for simpler techniques).
Solution 3
Note that the middle tile can be any of the four tiles. The white part of the middle tile points towards one of the corners, and for the white diamond to appear the three adjacent tiles must all be perfect. Thus, the solution is
~aayr
Video Solution 1 by OmegaLearn (Using Cool Probability Technique)
Animated Video Solution
~Star League (https://starleague.us)
See Also
2023 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 |
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