MathDB
1990 AMC 12 #26

Source:

December 30, 2011
AMC

Problem Statement

Ten people form a circle. Each picks a number and tells it to the two neighbors adjacent to him in the circle. Then each person computes and announces the average of the numbers of his two neighbors. The figure shows the average announced by each person (not the original number the person picked). The number picked by the person who announced the average 66 was [asy] label("(1)", (0,.9)); label("(2)", (.4,.65)); label("(3)", (.8,.25)); label("(4)", (.8,-.2)); label("(5)", (.4,-.65)); label("(6)", (0,-.9)); label("(7)", (-.4,-.65)); label("(8)", (-.8,-.2)); label("(9)", (-.8,.25)); label("(10)", (-.4,.65)); [/asy] <spanclass=latexbold>(A)</span> 1<spanclass=latexbold>(B)</span> 5<spanclass=latexbold>(C)</span> 6<spanclass=latexbold>(D)</span> 10<spanclass=latexbold>(E)</span> not uniquely determined from the given information <span class='latex-bold'>(A)</span>\ 1 \qquad<span class='latex-bold'>(B)</span>\ 5 \qquad<span class='latex-bold'>(C)</span>\ 6 \qquad<span class='latex-bold'>(D)</span>\ 10 \qquad<span class='latex-bold'>(E)</span>\ \text{not uniquely determined from the given information}