Difference between revisions of "2019 AMC 8 Problems/Problem 13"

Revision as of 15:58, 19 August 2020

Problem 13

A palindrome is a number that has the same value when read from left to right or from right to left. (For example 12321 is a palindrome.) Let $N$ be the least three-digit integer which is not a palindrome but which is the sum of three distinct two-digit palindromes. What is the sum of the digits of $N$ ?

$\textbf{(A) }2\qquad\textbf{(B) }3\qquad\textbf{(C) }4\qquad\textbf{(D) }5\qquad\textbf{(E) }6$

Solution 1

Note that the only positive 2-digit palindromes are multiples of 11, namely $11, 22, \ldots, 99$ . Since $N$ is the sum of 2-digit palindromes, $N$ is necessarily a multiple of 11. The smallest 3-digit multiple of 11 which is not a palindrome is 110, so $N=110$ is a candidate solution. We must check that 110 can be written as the sum of three distinct 2-digit palindromes; this suffices as $110=77+22+11$ . Then $N = 110$ , and the sum of the digits of $N$ is $1+1+0 = \boxed{\textbf{(A) }2}$ .

Solution 2

Associated video - https://www.youtube.com/watch?v=bOnNFeZs7S8

Video Solution - https://youtu.be/Lw8fSbX_8FU (Also explains problems 11-20)

2019 AMC 8 (Problems • Answer Key • Resources)
Preceded by Problem 12	Followed by Problem 14
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.

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 ==Solution 2==
 Associated video - https://www.youtube.com/watch?v=bOnNFeZs7S8
+Video Solution - https://youtu.be/Lw8fSbX_8FU (Also explains problems 11-20)
 ==See Also==

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Difference between revisions of "2019 AMC 8 Problems/Problem 13"

Revision as of 15:58, 19 August 2020

Contents

Problem 13

Solution 1

Solution 2

See Also