Difference between revisions of "2023 AMC 8 Problems/Problem 16"

(Solution 9 (Common Sense, Fast))
(Solution 4 (Brute Force))
 
(18 intermediate revisions by 8 users not shown)
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<math>\textbf{(E)}~134\text{ Ps, }133\text{ Qs, }133\text{ Rs}</math>
 
<math>\textbf{(E)}~134\text{ Ps, }133\text{ Qs, }133\text{ Rs}</math>
  
== Solution 1 (Logic/Finding Patterns)==
+
== Solution 1 (Finding a Pattern)==
  
In our <math>5 \times 5</math> grid we can see there are <math>8,9</math> and <math>8</math> of the letters <math>\text{P}, \text{Q},</math> and <math>\text{R}</math>’s respectively. We can see our pattern between each is <math>x, x+1,</math> and <math>x</math> for the <math>\text{P}, \text{Q},</math> and <math>\text{R}</math>’s respectively. This such pattern will follow in our bigger example, so we can see that the only answer choice which satisfies this condition is <math>\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.</math>
+
In our <math>5\times5</math> grid, there are <math>8,9</math> and <math>8</math> of the letters <math>\text{P}, \text{Q},</math> and <math>\text{R}</math>, respectively, and in a <math>2\times2</math> grid, there are <math>1,2</math> and <math>1</math> of the letters <math>\text{P}, \text{Q},</math> and <math>\text{R}</math>, respectively. We see that in both grids, there are <math>x, x+1,</math> and <math>x</math> of the <math>\text{P}, \text{Q},</math> and <math>\text{R}</math>, respectively. This is because in any <math>n\times n</math> grid with <math>n\equiv2\pmod3</math>, there are <math>x, x+1,</math> and <math>x</math> of the <math>\text{P}, \text{Q},</math> and <math>\text{R}</math>, respectively. We can see that the only answer choice which satisfies this condition is <math>\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.</math>
  
(Note: you could also "cheese" this problem by brute force/listing out all of the letters horizontally in a single line and looking at the repeating pattern. Refer to solution 4)
+
~CoOlPoTaToEs, apex304, SohumUttamchandani, wuwang2002, TaeKim, Cxrupptedpat, Nivaar
 
 
~apex304, SohumUttamchandani, wuwang2002, TaeKim, Cxrupptedpat, Nivaar
 
  
 
== Solution 2 ==
 
== Solution 2 ==
  
We think about which letter is in the diagonal with <math>20</math> of a letter. We find that it is <math>2(2 + 5 + 8 + 11 + 14 + 17) + 20 = 134.</math> The rest of the grid with the <math>\text{P}</math>'s and <math>\text{R}</math>'s is symmetric. Therefore, the answer is <math>\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.</math>
+
Since <math>20\equiv2\pmod3</math> and <math>\text{Q}</math> is in the 2nd diagonal, it is also in the 20th diagonal, and so we find that there are <math>2(2 + 5 + 8 + 11 + 14 + 17) + 20 = 134 \text{Qs}</math>. Since all the <math>\text{P}</math>'s and <math>\text{R}</math>'s are symmetric, the answer is <math>\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.</math>
  
 
~[[User:ILoveMath31415926535|ILoveMath31415926535]]
 
~[[User:ILoveMath31415926535|ILoveMath31415926535]]
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== Solution 6 (Modular Arithmetic)==
 
== Solution 6 (Modular Arithmetic)==
  
Note that the a different letter is always to either the left and right to one letter (there will never be two of the same letter in a row or column).
+
If a letter is in a horizontal position <math>k</math>, then that same letter will appear in position <math>k+3m</math>, for a positive integer <math>m</math>. In other words, all positions congruent to <math>k</math> modulo <math>3</math> will have the same letter as <math>p</math>.  
 
 
It follows that if a letter is in a horizontal position <math>k</math>, then that same letter will appear in position <math>k+3m</math>, for a positive integer <math>m</math>. In other words, all positions congruent to <math>k</math> modulo <math>3</math> will have the same letter as <math>p</math>.  
 
  
 
Since <math>p</math> is in position <math>1</math>, <math>p</math> will be in every position congruent to <math>1 \pmod 3</math>. There are <math>7</math> numbers less than or equal to <math>20</math> that satisfy this restraint. There are also <math>7</math> numbers less than or equal to <math>2</math> that are congruent to <math>2 \pmod 3</math>, but only <math>6</math> that are multiples of <math>3</math>.  
 
Since <math>p</math> is in position <math>1</math>, <math>p</math> will be in every position congruent to <math>1 \pmod 3</math>. There are <math>7</math> numbers less than or equal to <math>20</math> that satisfy this restraint. There are also <math>7</math> numbers less than or equal to <math>2</math> that are congruent to <math>2 \pmod 3</math>, but only <math>6</math> that are multiples of <math>3</math>.  
  
In <math>p</math>'s case, it will appear <math>7</math> times in row one, only <math>6</math> in row <math>2</math> (as its first appearence is in position <math>3</math>), and <math>7</math> in row <math>3</math>. So in the first <math>3</math> rows, <math>P</math> appears <math>20</math> times.  
+
In <math>p</math>'s case, it will appear <math>7</math> times in row one, only <math>6</math> in row <math>2</math> (as its first appearance is in position <math>3</math>), and <math>7</math> in row <math>3</math>. So in the first <math>3</math> rows, <math>P</math> appears <math>20</math> times.  
  
 
Therefore, in the first <math>18</math> rows, <math>P</math> appears <math>20\cdot 6 = 120</math> times. Row <math>19</math> looks identical to row <math>1</math>, as <math>19\equiv 1\pmod 3</math>, so <math>P</math> appears in row <math>19</math> <math>7</math> times. It follows that <math>P</math> appears in row <math>20</math> <math>6</math> times. There are <math>134 P</math>s.  
 
Therefore, in the first <math>18</math> rows, <math>P</math> appears <math>20\cdot 6 = 120</math> times. Row <math>19</math> looks identical to row <math>1</math>, as <math>19\equiv 1\pmod 3</math>, so <math>P</math> appears in row <math>19</math> <math>7</math> times. It follows that <math>P</math> appears in row <math>20</math> <math>6</math> times. There are <math>134 P</math>s.  
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~andyluo
 
~andyluo
  
==Solution 8 (Patterns)==
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==Solution 8 (Intuitive, Fastest)==
NOTE THAT THIS SOLUTION IS VERY SIMILAR TO SOLUTION 1.
+
When we find the letters at the corners, we see that there are 2 other corners with Q's and 1 with R. There are 2 corners with Q and 1 with P and R. Therefore, it makes sense that there should be more Q's than other letters. Only <math>\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}</math> has more Q's than other letters.
 +
 
 +
<b>Only do it this way if there are 30 seconds left on the clock, as it may not always work!</b>
  
We can start by writing down the <math>P</math>s, <math>Q</math>s, and <math>R</math>s for <math>5\times5, 4\times4, 3\times3,</math> and <math>2\times2</math> squares:
+
==Solution 9 (Think and Label)==
 +
Since there are <math>3</math> letters, there must be a multiple of 3 for the height of the array for the amount of letters to be the same. However, there is one less (<math>21-1=20</math>) so there will be one less letter in each column compared to the other two. Looking at the diagram, the first column starts with a <math>P</math> then a <math>Q</math>. Since it will miss the third letter, <math>R</math>, we write this as <math>-R</math>. We do this process for the remaining 20 columns, and applying the same logic if the first three are <math>-R</math>, <math>-P</math> and <math>-Q</math>, there will be one less <math>-Q</math> meaning that there will be an extra <math>Q</math>. The only answer that has in extra <math>Q</math> is <math>\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}</math>
  
* <math>5\times5: \ 8,9,8</math>
+
~Blue_Kite
* <math>4\times4: \ 6,5,5</math>
 
* <math>3\times3: \ 3,3,3</math>
 
* <math>2\times2: \ 1,2,1</math>
 
  
We know that all the squares with side lengths that are multiples of <math>3</math> will have an equal number of <math>P</math>s, <math>Q</math>s, and <math>R</math>s, so we don't worry too much about the <math>3\times3.</math> From the other ones, we can easily see that they are all <math>x, x+1,</math> and <math>x.</math> Using this, we find the only option that provides this format, which is <math>\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.</math>
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== Video Solution 1 by Math-X ==
  
~CoOlPoTaToEs
+
https://youtu.be/Ku_c1YHnLt0?si=Xxe3CXtrXQYGSYik&t=3081
  
==Solution 9 (Common Sense, Fast)==
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== Video Solution 2 by CoolMathProblems ==
When we extend to find the letters at the corners, there are 2 vertices with Q's and 1 with each other letter. Therefore, it makes sense that there should be more Q's than other letters.
 
(Only do it this way if there are 30 seconds left on the clock).
 
  
==Video Solution (Solve under 60 seconds!!!)==
+
https://youtu.be/_huZfhiCBN8
https://youtu.be/6O5UXi-Jwv4?si=KvvABit-3-ZtX7Qa&t=731
 
  
~hsnacademy
+
== Video Solution 3 by hnsacademy ==
  
==Video Solution by Math-X (Let's first Understand the question)==
+
https://youtu.be/zntZrtsnyxc?si=nM5eWOwNU6HRdleZ&t=1453
https://youtu.be/Ku_c1YHnLt0?si=Xxe3CXtrXQYGSYik&t=3081
 
  
~Math-X
+
== Video Solution 4 ==
  
==Video Solution (CREATIVE THINKING!!!)==
 
 
https://youtu.be/3DTwjLe0Pw0
 
https://youtu.be/3DTwjLe0Pw0
  
 
~Education, the Study of Everything
 
~Education, the Study of Everything
  
==Video Solution (Animated)==
+
== Video Solution 5 ==
 +
 
 
https://youtu.be/1tnMR0lNEFY
 
https://youtu.be/1tnMR0lNEFY
  
~Star League (https://starleague.us)
+
~[//starleague.us Star League]
 +
 
 +
== Video Solution 6 by OmegaLearn (Using Cyclic Patterns) ==
  
==Video Solution by OmegaLearn (Using Cyclic Patterns)==
 
 
https://youtu.be/83FnFhe4QgQ
 
https://youtu.be/83FnFhe4QgQ
  
==Video Solution by Magic Square==
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== Video Solution 7 by Magic Square ==
 +
 
 
https://youtu.be/-N46BeEKaCQ?t=3990
 
https://youtu.be/-N46BeEKaCQ?t=3990
==Video Solution by Interstigation==
+
 
 +
== Video Solution 8 by Interstigation ==
 +
 
 
https://youtu.be/DBqko2xATxs&t=1845
 
https://youtu.be/DBqko2xATxs&t=1845
  
==Video Solution by WhyMath==
+
== Video Solution 9 by WhyMath ==
 +
 
 
https://youtu.be/iMhqlz0-ce0
 
https://youtu.be/iMhqlz0-ce0
  
~savannahsolver
+
== Video Solution 10 ==
  
==Video Solution by harungurcan==
 
 
https://www.youtube.com/watch?v=jtHe6yLBz-4&t=20s
 
https://www.youtube.com/watch?v=jtHe6yLBz-4&t=20s
  
~harungurcan
+
== Video Solution 11 by Dr. David ==
  
==Video Solution by Dr. David==
 
 
https://youtu.be/yeXuFQHYU7k
 
https://youtu.be/yeXuFQHYU7k
  
==See Also==  
+
==See Also==
 +
 
 
{{AMC8 box|year=2023|num-b=15|num-a=17}}
 
{{AMC8 box|year=2023|num-b=15|num-a=17}}
 
{{MAA Notice}}
 
{{MAA Notice}}

Latest revision as of 13:59, 19 January 2025

Problem

The letters $\text{P}, \text{Q},$ and $\text{R}$ are entered into a $20\times20$ table according to the pattern shown below. How many $\text{P}$s, $\text{Q}$s, and $\text{R}$s will appear in the completed table? [asy] /* Made by MRENTHUSIASM, Edited by Kante314 */ usepackage("mathdots"); size(5cm); draw((0,0)--(6,0),linewidth(1.5)+mediumgray); draw((0,1)--(6,1),linewidth(1.5)+mediumgray); draw((0,2)--(6,2),linewidth(1.5)+mediumgray); draw((0,3)--(6,3),linewidth(1.5)+mediumgray); draw((0,4)--(6,4),linewidth(1.5)+mediumgray); draw((0,5)--(6,5),linewidth(1.5)+mediumgray);  draw((0,0)--(0,6),linewidth(1.5)+mediumgray); draw((1,0)--(1,6),linewidth(1.5)+mediumgray); draw((2,0)--(2,6),linewidth(1.5)+mediumgray); draw((3,0)--(3,6),linewidth(1.5)+mediumgray); draw((4,0)--(4,6),linewidth(1.5)+mediumgray); draw((5,0)--(5,6),linewidth(1.5)+mediumgray);  label(scale(.9)*"\textsf{P}", (.5,.5)); label(scale(.9)*"\textsf{Q}", (.5,1.5)); label(scale(.9)*"\textsf{R}", (.5,2.5)); label(scale(.9)*"\textsf{P}", (.5,3.5)); label(scale(.9)*"\textsf{Q}", (.5,4.5)); label("$\vdots$", (.5,5.6));  label(scale(.9)*"\textsf{Q}", (1.5,.5)); label(scale(.9)*"\textsf{R}", (1.5,1.5)); label(scale(.9)*"\textsf{P}", (1.5,2.5)); label(scale(.9)*"\textsf{Q}", (1.5,3.5)); label(scale(.9)*"\textsf{R}", (1.5,4.5)); label("$\vdots$", (1.5,5.6));  label(scale(.9)*"\textsf{R}", (2.5,.5)); label(scale(.9)*"\textsf{P}", (2.5,1.5)); label(scale(.9)*"\textsf{Q}", (2.5,2.5)); label(scale(.9)*"\textsf{R}", (2.5,3.5)); label(scale(.9)*"\textsf{P}", (2.5,4.5)); label("$\vdots$", (2.5,5.6));  label(scale(.9)*"\textsf{P}", (3.5,.5)); label(scale(.9)*"\textsf{Q}", (3.5,1.5)); label(scale(.9)*"\textsf{R}", (3.5,2.5)); label(scale(.9)*"\textsf{P}", (3.5,3.5)); label(scale(.9)*"\textsf{Q}", (3.5,4.5)); label("$\vdots$", (3.5,5.6));  label(scale(.9)*"\textsf{Q}", (4.5,.5)); label(scale(.9)*"\textsf{R}", (4.5,1.5)); label(scale(.9)*"\textsf{P}", (4.5,2.5)); label(scale(.9)*"\textsf{Q}", (4.5,3.5)); label(scale(.9)*"\textsf{R}", (4.5,4.5)); label("$\vdots$", (4.5,5.6));  label(scale(.9)*"$\dots$", (5.5,.5)); label(scale(.9)*"$\dots$", (5.5,1.5)); label(scale(.9)*"$\dots$", (5.5,2.5)); label(scale(.9)*"$\dots$", (5.5,3.5)); label(scale(.9)*"$\dots$", (5.5,4.5)); label(scale(.9)*"$\iddots$", (5.5,5.6)); [/asy] $\textbf{(A)}~132\text{ Ps, }134\text{ Qs, }134\text{ Rs}$

$\textbf{(B)}~133\text{ Ps, }133\text{ Qs, }134\text{ Rs}$

$\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}$

$\textbf{(D)}~134\text{ Ps, }132\text{ Qs, }134\text{ Rs}$

$\textbf{(E)}~134\text{ Ps, }133\text{ Qs, }133\text{ Rs}$

Solution 1 (Finding a Pattern)

In our $5\times5$ grid, there are $8,9$ and $8$ of the letters $\text{P}, \text{Q},$ and $\text{R}$, respectively, and in a $2\times2$ grid, there are $1,2$ and $1$ of the letters $\text{P}, \text{Q},$ and $\text{R}$, respectively. We see that in both grids, there are $x, x+1,$ and $x$ of the $\text{P}, \text{Q},$ and $\text{R}$, respectively. This is because in any $n\times n$ grid with $n\equiv2\pmod3$, there are $x, x+1,$ and $x$ of the $\text{P}, \text{Q},$ and $\text{R}$, respectively. We can see that the only answer choice which satisfies this condition is $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.$

~CoOlPoTaToEs, apex304, SohumUttamchandani, wuwang2002, TaeKim, Cxrupptedpat, Nivaar

Solution 2

Since $20\equiv2\pmod3$ and $\text{Q}$ is in the 2nd diagonal, it is also in the 20th diagonal, and so we find that there are $2(2 + 5 + 8 + 11 + 14 + 17) + 20 = 134 \text{Qs}$. Since all the $\text{P}$'s and $\text{R}$'s are symmetric, the answer is $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.$

~ILoveMath31415926535

Solution 3

Notice that rows $x$ and $x+3$ are the same, for any $1 \leq x \leq 17.$ Additionally, rows $1, 2,$ and $3$ collectively contain the same number of $\text{P}$s, $\text{Q}$s, and $\text{R}$s, because the letters are just substituted for one another. Therefore, the number of $\text{P}$s, $\text{Q}$s, and $\text{R}$s in the first $18$ rows is $120$. The first row has $7$ $\text{P}$s, $7$ $\text{Q}$s, and $6$ $\text{R}$s, and the second row has $6$ $\text{P}$s, $7$ $\text{Q}$s, and $7$ $\text{R}$s. Adding these up, we obtain $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}$.

~mathboy100

Solution 4 (Brute-Force)

From the full diagram below, the answer is $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.$ [asy] /* Made by MRENTHUSIASM, Edited by Kante314 */ usepackage("mathdots"); size(16.666cm);  for (int y = 0; y<=20; ++y) { 	for (int x = 0; x<=20; ++x) {    		draw((x,0)--(x,20),linewidth(1.5)+mediumgray); 		draw((0,y)--(20,y),linewidth(1.5)+mediumgray); 	} }  void drawDiagonal(string s, pair p) { 	while (p.x >= 0 && p.x < 20 && p.y >= 0 && p.y < 20) {     	label(scale(.9)*("\textsf{" + s + "}"),p);         p += (1,-1);     } }  drawDiagonal("P", (0.5,0.5)); drawDiagonal("Q", (0.5,1.5)); drawDiagonal("R", (0.5,2.5)); drawDiagonal("P", (0.5,3.5)); drawDiagonal("Q", (0.5,4.5)); drawDiagonal("R", (0.5,5.5)); drawDiagonal("P", (0.5,6.5)); drawDiagonal("Q", (0.5,7.5)); drawDiagonal("R", (0.5,8.5));  drawDiagonal("P", (0.5,9.5)); drawDiagonal("Q", (0.5,10.5)); drawDiagonal("R", (0.5,11.5)); drawDiagonal("P", (0.5,12.5)); drawDiagonal("Q", (0.5,13.5)); drawDiagonal("R", (0.5,14.5)); drawDiagonal("P", (0.5,15.5)); drawDiagonal("Q", (0.5,16.5)); drawDiagonal("R", (0.5,17.5)); drawDiagonal("P", (0.5,18.5)); drawDiagonal("Q", (0.5,19.5));  drawDiagonal("R", (1.5,19.5));  drawDiagonal("P", (2.5,19.5)); drawDiagonal("Q", (3.5,19.5)); drawDiagonal("R", (4.5,19.5));  drawDiagonal("P", (5.5,19.5)); drawDiagonal("Q", (6.5,19.5)); drawDiagonal("R", (7.5,19.5));  drawDiagonal("P", (8.5,19.5)); drawDiagonal("Q", (9.5,19.5)); drawDiagonal("R", (10.5,19.5));  drawDiagonal("P", (11.5,19.5)); drawDiagonal("Q", (12.5,19.5)); drawDiagonal("R", (13.5,19.5));  drawDiagonal("P", (14.5,19.5)); drawDiagonal("Q", (15.5,19.5)); drawDiagonal("R", (16.5,19.5));  drawDiagonal("P", (17.5,19.5)); drawDiagonal("Q", (18.5,19.5)); drawDiagonal("R", (19.5,19.5)); [/asy] This solution is extremely time-consuming and error-prone. Please do not try it in a real competition unless you have no other options.

~MRENTHUSIASM

Solution 5

This solution refers to the full diagram in Solution 4.

Note the $\text{Q}$ diagonals are symmetric. The $\text{R}$ and $\text{P}$ diagonals are not symmetric, but are reflections of each other about the $\text{Q}$ diagonals:

  • The upper $\text{Q}$ diagonal of length $2$ is surrounded by a $\text{P}$ diagonal of length $3$ and an $\text{R}$ diagonal of length $1.$
  • The lower $\text{Q}$ diagonal of length $2$ is surrounded by a $\text{P}$ diagonal of length $1$ and an $\text{R}$ diagonal of length $3.$

When looking at a pair of $Q$ diagonals of the same length $x,$ there is a total of $2x$ $\text{R}$s and $\text{P}$s next to these $2$ diagonals.

The main diagonal of $20$ $\text{Q}$s has $19$ $\text{P}$s and $19$ $\text{R}$s next to it. Thus, the total is $x+1$ $\text{Q}$s, $x$ $\text{P}$s, $x$ $\text{R}$s. Therefore, the answer is $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.$

~ERMSCoach

Solution 6 (Modular Arithmetic)

If a letter is in a horizontal position $k$, then that same letter will appear in position $k+3m$, for a positive integer $m$. In other words, all positions congruent to $k$ modulo $3$ will have the same letter as $p$.

Since $p$ is in position $1$, $p$ will be in every position congruent to $1 \pmod 3$. There are $7$ numbers less than or equal to $20$ that satisfy this restraint. There are also $7$ numbers less than or equal to $2$ that are congruent to $2 \pmod 3$, but only $6$ that are multiples of $3$.

In $p$'s case, it will appear $7$ times in row one, only $6$ in row $2$ (as its first appearance is in position $3$), and $7$ in row $3$. So in the first $3$ rows, $P$ appears $20$ times.

Therefore, in the first $18$ rows, $P$ appears $20\cdot 6 = 120$ times. Row $19$ looks identical to row $1$, as $19\equiv 1\pmod 3$, so $P$ appears in row $19$ $7$ times. It follows that $P$ appears in row $20$ $6$ times. There are $134 P$s.

Counting $Q$s is nearly identical, but $Q$ begins in position $2$. In the first $18$ rows, there are an identical amount of $Q$s too, namely $6(7+7+6) = 120$. However, by a similar argument to $P$, $Q$ appears $7+7$ times in the last two rows; because row $20$ is the same as row $2$, $Q$ appears in position $1$, and thus $7$ times.

Therefore, there are $120+14 = 134$ $Q$s and $133$ $P$. We could go through a similar argument for $R$, or note that the only answer choice with these two options is $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.$

-Benedict T (countmath1)

Solution 7 (Answer Choices, Fast)

We can first observe that $P$ shows on diagonals increasing or decreasing by $3.$

It starts at $1,4,7,9...$ and increases in the form $3x-2$. Using our answer choices, $(B)$ and $(C)$ are the only fits.

$Q$ is like this as well, increasing $2,5,8,11....$ This means $Q$ has to be in the form of $3x-1.$ Testing this out leads us with $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}.$

~andyluo

Solution 8 (Intuitive, Fastest)

When we find the letters at the corners, we see that there are 2 other corners with Q's and 1 with R. There are 2 corners with Q and 1 with P and R. Therefore, it makes sense that there should be more Q's than other letters. Only $\boxed{\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}}$ has more Q's than other letters.

Only do it this way if there are 30 seconds left on the clock, as it may not always work!

Solution 9 (Think and Label)

Since there are $3$ letters, there must be a multiple of 3 for the height of the array for the amount of letters to be the same. However, there is one less ($21-1=20$) so there will be one less letter in each column compared to the other two. Looking at the diagram, the first column starts with a $P$ then a $Q$. Since it will miss the third letter, $R$, we write this as $-R$. We do this process for the remaining 20 columns, and applying the same logic if the first three are $-R$, $-P$ and $-Q$, there will be one less $-Q$ meaning that there will be an extra $Q$. The only answer that has in extra $Q$ is $\textbf{(C)}~133\text{ Ps, }134\text{ Qs, }133\text{ Rs}$

~Blue_Kite

Video Solution 1 by Math-X

https://youtu.be/Ku_c1YHnLt0?si=Xxe3CXtrXQYGSYik&t=3081

Video Solution 2 by CoolMathProblems

https://youtu.be/_huZfhiCBN8

Video Solution 3 by hnsacademy

https://youtu.be/zntZrtsnyxc?si=nM5eWOwNU6HRdleZ&t=1453

Video Solution 4

https://youtu.be/3DTwjLe0Pw0

~Education, the Study of Everything

Video Solution 5

https://youtu.be/1tnMR0lNEFY

~Star League

Video Solution 6 by OmegaLearn (Using Cyclic Patterns)

https://youtu.be/83FnFhe4QgQ

Video Solution 7 by Magic Square

https://youtu.be/-N46BeEKaCQ?t=3990

Video Solution 8 by Interstigation

https://youtu.be/DBqko2xATxs&t=1845

Video Solution 9 by WhyMath

https://youtu.be/iMhqlz0-ce0

Video Solution 10

https://www.youtube.com/watch?v=jtHe6yLBz-4&t=20s

Video Solution 11 by Dr. David

https://youtu.be/yeXuFQHYU7k

See Also

2023 AMC 8 (ProblemsAnswer KeyResources)
Preceded by
Problem 15
Followed by
Problem 17
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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