MathDB
P23 [Combinatorics] - Turkish NMO 1st Round - 2003

Source:

May 18, 2014

Problem Statement

Ayse knows the weights of nine balls with different colors are 1,2,,91,2,\cdots, 9 grams, but she doesn't know the weight of a specific ball. But Baris knows the weight of each ball. Baris wants to prove his knowledge to Ayse. There is a double pan balance which shows the heavier pan and the difference of the two pans. At least how many weighs are required for proof of Ali's knowledge?
<spanclass=latexbold>(A)</span> 2<spanclass=latexbold>(B)</span> 3<spanclass=latexbold>(C)</span> 4<spanclass=latexbold>(D)</span> 5<spanclass=latexbold>(E)</span> 6 <span class='latex-bold'>(A)</span>\ 2 \qquad<span class='latex-bold'>(B)</span>\ 3 \qquad<span class='latex-bold'>(C)</span>\ 4 \qquad<span class='latex-bold'>(D)</span>\ 5 \qquad<span class='latex-bold'>(E)</span>\ 6