Turkish NMO First Round - 2012 Problem - 32 {Combinatorics}
Source:
July 1, 2012
Problem Statement
How many permutations (a1,a2,…,a10) of 1,2,3,4,5,6,7,8,9,10 satisfy ∣a1−1∣+∣a2−2∣+⋯+∣a10−10∣=4 ?<spanclass=′latex−bold′>(A)</span>60<spanclass=′latex−bold′>(B)</span>52<spanclass=′latex−bold′>(C)</span>50<spanclass=′latex−bold′>(D)</span>44<spanclass=′latex−bold′>(E)</span>36