Difference between revisions of "2020 AMC 12B Problems/Problem 15"
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There are <math>10</math> people standing equally spaced around a circle. Each person knows exactly <math>3</math> of the other <math>9</math> people: the <math>2</math> people standing next to her or him,as well as the person directly across the circle. How many ways are there for the <math>10</math> people to split up into <math>5</math> pairs so that the members of each pair know each other? | There are <math>10</math> people standing equally spaced around a circle. Each person knows exactly <math>3</math> of the other <math>9</math> people: the <math>2</math> people standing next to her or him,as well as the person directly across the circle. How many ways are there for the <math>10</math> people to split up into <math>5</math> pairs so that the members of each pair know each other? | ||
| − | <math>(A) | + | <math>\textbf{(A)}\ 11 \qquad\textbf{(B)}\ 12 \qquad\textbf{(C)}\ 13 \qquad\textbf{(D)}\ 14 \qquad\textbf{(E)}\ 15</math> |
Revision as of 21:20, 7 February 2020
Problem
There are 
people standing equally spaced around a circle. Each person knows exactly 
of the other 
people: the 
people standing next to her or him,as well as the person directly across the circle. How many ways are there for the people to split up into 
pairs so that the members of each pair know each other?
