Problem
COM-B1-M06-P005 Number of Minuses
#5
★☆☆☆☆ Level 1 of 5
There are \(8\) plus signs on the board. In one move, two signs may be changed to the opposite signs. Can exactly \(3\) minuses be obtained?
The parity of the number of minuses is preserved.
Changing two signs changes the number of minuses by \(-2\), \(0\), or \(2\). Its parity is preserved. Initially it is \(0\), but the target is \(3\), impossible.
Parity of signs.