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2022 AMC 8 Problems/Problem 12: Difference between revisions

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The arrows on the two spinners shown below are spun. Let the number <math>N</math>  equal <math>10</math> times the number on Spinner <math>\text{A}</math>, added to the number on Spinner <math>\text{B}</math>. What is the probability that <math>N</math> is a perfect square number?
The arrows on the two spinners shown below are spun. Let the number <math>N</math>  equal <math>10</math> times the number on Spinner <math>\text{A}</math>, added to the number on Spinner <math>\text{B}</math>. What is the probability that <math>N</math> is a perfect square number?
<asy>
<asy>
//diagram by pog give me 1 billion dollars for this
//diagram by pog
size(6cm);
size(6cm);
usepackage("mathptmx");
usepackage("mathptmx");
Line 48: Line 48:


~ligonmathkid2
~ligonmathkid2
==Video Solution (A Clever Explanation You’ll Get Instantly)==
https://youtu.be/tYWp6fcUAik?si=V8hv_zOn_zYOi9E5&t=1458
~hsnacademy
==Video Solution by Math-X (First understand the problem!!!)==
https://youtu.be/oUEa7AjMF2A?si=NvktZSXqcd8LE9yU&t=1604
~Math-X
==Video Solution (CREATIVE THINKING!!!)==
https://youtu.be/Flq6oB23_WM
~Education, the Study of Everything


==Video Solution==
==Video Solution==
Line 63: Line 77:


~savannahsolver
~savannahsolver
==Video Solution==
https://youtu.be/U6eqFrD7BXA
~harungurcan
==Video Solution by Dr. David==
https://youtu.be/VvSstZB3xlI


==See Also==  
==See Also==  
{{AMC8 box|year=2022|num-b=11|num-a=13}}
{{AMC8 box|year=2022|num-b=11|num-a=13}}
{{MAA Notice}}
{{MAA Notice}}
[[Category:Introductory Probability Problems]]

Latest revision as of 16:39, 4 June 2025

Problem

The arrows on the two spinners shown below are spun. Let the number $N$ equal $10$ times the number on Spinner $\text{A}$, added to the number on Spinner $\text{B}$. What is the probability that $N$ is a perfect square number? [asy] //diagram by pog size(6cm); usepackage("mathptmx"); filldraw(arc((0,0), r=4, angle1=0, angle2=90)--(0,0)--cycle,mediumgray*0.5+gray*0.5); filldraw(arc((0,0), r=4, angle1=90, angle2=180)--(0,0)--cycle,lightgray); filldraw(arc((0,0), r=4, angle1=180, angle2=270)--(0,0)--cycle,mediumgray); filldraw(arc((0,0), r=4, angle1=270, angle2=360)--(0,0)--cycle,lightgray*0.5+mediumgray*0.5); label("$5$", (-1.5,1.7)); label("$6$", (1.5,1.7)); label("$7$", (1.5,-1.7)); label("$8$", (-1.5,-1.7)); label("Spinner A", (0, -5.5)); filldraw(arc((12,0), r=4, angle1=0, angle2=90)--(12,0)--cycle,mediumgray*0.5+gray*0.5); filldraw(arc((12,0), r=4, angle1=90, angle2=180)--(12,0)--cycle,lightgray); filldraw(arc((12,0), r=4, angle1=180, angle2=270)--(12,0)--cycle,mediumgray); filldraw(arc((12,0), r=4, angle1=270, angle2=360)--(12,0)--cycle,lightgray*0.5+mediumgray*0.5); label("$1$", (10.5,1.7)); label("$2$", (13.5,1.7)); label("$3$", (13.5,-1.7)); label("$4$", (10.5,-1.7)); label("Spinner B", (12, -5.5)); [/asy] $\textbf{(A)} ~\dfrac{1}{16}\qquad\textbf{(B)} ~\dfrac{1}{8}\qquad\textbf{(C)} ~\dfrac{1}{4}\qquad\textbf{(D)} ~\dfrac{3}{8}\qquad\textbf{(E)} ~\dfrac{1}{2}$

Solution 1

First, we calculate that there are a total of $4\cdot4=16$ possibilities. Now, we list all of two-digit perfect squares. $64$ and $81$ are the only ones that can be made using the spinner. Consequently, there is a $\frac{2}{16}=\boxed{\textbf{(B) }\dfrac{1}{8}}$ probability that the number formed by the two spinners is a perfect square.

~MathFun1000

Solution 2

There are $4 \cdot 4 = 16$ total possibilities of $N$. We know $N=10A+B$, which $A$ is a number from spinner $A$, and $B$ is a number from spinner $B$. Also, notice that there are no perfect squares in the $50$s or $70$s, so only $4-2=2$ values of N work, namely $64$ and $81$. Hence, $\frac{2}{16}=\boxed{\textbf{(B) }\dfrac{1}{8}}$.

~MrThinker

Solution 3

Just try them!

  • If we spin a 5 on the first spinner, there are no solutions.
  • If we spin a 6 on the first spinner, there is one solution (64).
  • If we spin a 7 on the first spinner, there are no solutions.
  • If we spin an 8 on the first spinner, there is one solution (81).

Therefore, there are 2 solutions and $4 \cdot 4 = 16$ total possibilities, so \[\frac{2}{16} = \boxed{\textbf{(B) }\dfrac{1}{8}}\]

~ligonmathkid2

Video Solution (A Clever Explanation You’ll Get Instantly)

https://youtu.be/tYWp6fcUAik?si=V8hv_zOn_zYOi9E5&t=1458 ~hsnacademy

Video Solution by Math-X (First understand the problem!!!)

https://youtu.be/oUEa7AjMF2A?si=NvktZSXqcd8LE9yU&t=1604

~Math-X

Video Solution (CREATIVE THINKING!!!)

https://youtu.be/Flq6oB23_WM

~Education, the Study of Everything

Video Solution

https://youtu.be/Ij9pAy6tQSg?t=1008

~Interstigation

Video Solution

https://youtu.be/p29Fe2dLGs8?t=58

~STEMbreezy

Video Solution

https://youtu.be/Wrbpq4D5F18

~savannahsolver

Video Solution

https://youtu.be/U6eqFrD7BXA

~harungurcan

Video Solution by Dr. David

https://youtu.be/VvSstZB3xlI

See Also

2022 AMC 8 (Problems • Answer Key • Resources)
Preceded by
Problem 11 		Followed by
Problem 13
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

These problems are copyrighted © by the Mathematical Association of America, as part of the American Mathematics Competitions. Error creating thumbnail: File missing

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