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Difference between revisions of "2010 AMC 12A Problems/Problem 6"
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== Problem ==
 
== Problem ==
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A <math>\text{palindrome}</math>, such as 83438, is a number that remains the same when its digits are reversed. The numbers <math>x</math> and <math>x+32</math> are three-digit and four-digit palindromes, respectively. What is the sum of the digits of <math>x</math>?
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A <math>\text{palindrome}</math>, such as <math>83438</math>, is a number that remains the same when its digits are reversed. The numbers <math>x</math> and <math>x+32</math> are three-digit and four-digit palindromes, respectively. What is the sum of the digits of <math>x</math>?
  
 
<math>\textbf{(A)}\ 20 \qquad \textbf{(B)}\ 21 \qquad \textbf{(C)}\ 22 \qquad \textbf{(D)}\ 23 \qquad \textbf{(E)}\ 24</math>
 
<math>\textbf{(A)}\ 20 \qquad \textbf{(B)}\ 21 \qquad \textbf{(C)}\ 22 \qquad \textbf{(D)}\ 23 \qquad \textbf{(E)}\ 24</math>
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===Solution 2===
 
===Solution 2===
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For <math>x+32</math> to be a four-digit number, <math>x</math> is in between <math>968</math> and <math>999</math>. The palindromes in this range are <math>969</math>, <math>979</math>, <math>989</math>, and <math>999</math>, so the sum of digits of <math>x</math> can be <math>24</math>, <math>25</math>, <math>26</math>, or <math>27</math>. Only <math>\boxed{\textbf{(E)}\ 24}</math> is an option, and upon checking, <math>x+32=1001</math> is indeed a palindrome.
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For <math>x+32</math> to be a four-digit number, <math>x</math> is in between <math>968</math> and <math>999</math>. The palindromes in this range are <math>969</math>, <math>979</math>, <math>989</math>, and <math>999</math>, so the sum of the digits of <math>x</math> can be <math>24</math>, <math>25</math>, <math>26</math>, or <math>27</math>. Only <math>\boxed{\textbf{(E)}\ 24}</math> is an option, and upon checking, <math>x+32=1001</math> is indeed a palindrome.
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===Solution 3===
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Since we know <math>x+32</math> to be <math>1 a a 1</math> and the only palindrome that works is <math>0 = a</math>, that means <math>x+32 = 1001</math>, and so <math>x = 1001 - 32 = 969</math>. So, <math>9</math> + <math>6</math> + <math>9</math> = <math>\boxed{\textbf{(E)}\ 24}</math>.
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~songmath20
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== Video Solution by OmegaLearn ==
 +
https://youtu.be/ZhAZ1oPe5Ds?t=1444
 +
 
 +
~ pi_is_3.14
 +
 
 +
== Video Solution ==
 +
https://youtu.be/IQj27LEQF4Y
 +
 
 +
~Education, the Study of Everything
  
 
== See also ==
 
== See also ==
 
{{AMC12 box|year=2010|num-b=5|num-a=7|ab=A}}
 
{{AMC12 box|year=2010|num-b=5|num-a=7|ab=A}}
 +
 +
{{AMC10 box|year=2010|num-b=8|num-a=10|ab=A}}
 +
  
 
[[Category:Introductory Algebra Problems]]
 
[[Category:Introductory Algebra Problems]]
 
{{MAA Notice}}
 
{{MAA Notice}}

Latest revision as of 03:51, 21 January 2023

The following problem is from both the 2010 AMC 12A #6 and 2010 AMC 10A #9, so both problems redirect to this page.

Problem

A $\text{palindrome}$, such as $83438$, is a number that remains the same when its digits are reversed. The numbers $x$ and $x+32$ are three-digit and four-digit palindromes, respectively. What is the sum of the digits of $x$?

$\textbf{(A)}\ 20 \qquad \textbf{(B)}\ 21 \qquad \textbf{(C)}\ 22 \qquad \textbf{(D)}\ 23 \qquad \textbf{(E)}\ 24$

Solution

Solution 1

$x$ is at most $999$, so $x+32$ is at most $1031$. The minimum value of $x+32$ is $1000$. However, the only palindrome between $1000$ and $1032$ is $1001$, which means that $x+32$ must be $1001$.

It follows that $x$ is $969$, so the sum of the digits is $\boxed{\textbf{(E)}\ 24}$.

Solution 2

For $x+32$ to be a four-digit number, $x$ is in between $968$ and $999$. The palindromes in this range are $969$, $979$, $989$, and $999$, so the sum of the digits of $x$ can be $24$, $25$, $26$, or $27$. Only $\boxed{\textbf{(E)}\ 24}$ is an option, and upon checking, $x+32=1001$ is indeed a palindrome.

Solution 3

Since we know $x+32$ to be $1 a a 1$ and the only palindrome that works is $0 = a$, that means $x+32 = 1001$, and so $x = 1001 - 32 = 969$. So, $9$ + $6$ + $9$ = $\boxed{\textbf{(E)}\ 24}$. ~songmath20

Video Solution by OmegaLearn

https://youtu.be/ZhAZ1oPe5Ds?t=1444

~ pi_is_3.14

Video Solution

https://youtu.be/IQj27LEQF4Y

~Education, the Study of Everything

See also

2010 AMC 12A (Problems • Answer Key • Resources)
Preceded by
Problem 5 		Followed by
Problem 7
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 AMC 12 Problems and Solutions
2010 AMC 10A (Problems • Answer Key • Resources)
Preceded by
Problem 8 		Followed by
Problem 10
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 AMC 10 Problems and Solutions

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