- Consider the "equation" $6145 - 1 = 6143$. Can you move two digits so as to create a valid equality?
- The equation $-127=-127$ is, of course, true. Suppose you were told again to move two digits as to leave a valid equation. Please note that you have to move two digits on the same side of this equation.
Moving means that you can change the position of any two digits independently, so that they still are a number/constant!
The moving doesn't require swapping of digits in both.
It is a part of mathematical puzzles asked in the puzzling contest at my college(coordinated by me).