Covering dots on a Table
In the Communications of the ACM, August 2008 "Puzzled" column, Peter Winkler asked the following question: On the table before us are 10 dots, and in our pocket are 10 $1 coins. Prove the coins can be placed on the table (no two overlapping) in such a way that all dots are covered. Figure 2 shows a valid placement of the c...