Difference between revisions of "2012 AMC 10B Problems/Problem 22"
(→Problem 22) |
(→Problem 22) |
||
| Line 1: | Line 1: | ||
==Problem 22== | ==Problem 22== | ||
| − | Let (<math>a1</math>, <math>a2</math>, ... <math>a10</math>) be a list of the first 10 positive integers such that for each 2 <math>i</math> | + | Let (<math>a1</math>, <math>a2</math>, ... <math>a10</math>) be a list of the first 10 positive integers such that for each <math>2\le </math>i<math> \le10</math> either <math>ai + 1</math> or <math>ai-1</math> or both appear somewhere before <math>ai</math> in the list. How many such lists are there? |
<math>\textbf{(A)}\ \120\qquad\textbf{(B)}\512\qquad\textbf{(C)}\ \1024\qquad\textbf{(D)}\ 181,440\qquad\textbf{(E)}\ \362,880</math> | <math>\textbf{(A)}\ \120\qquad\textbf{(B)}\512\qquad\textbf{(C)}\ \1024\qquad\textbf{(D)}\ 181,440\qquad\textbf{(E)}\ \362,880</math> | ||
Revision as of 01:00, 24 December 2012
Problem 22
Let (
, 
, ... 
) be a list of the first 10 positive integers such that for each 
i
either 
or 
or both appear somewhere before 
in the list. How many such lists are there?
$\textbf{(A)}\ \120\qquad\textbf{(B)}\512\qquad\textbf{(C)}\ \1024\qquad\textbf{(D)}\ 181,440\qquad\textbf{(E)}\ \362,880$ (Error compiling LaTeX. Unknown error_msg)
