The numbers +1 and -1 are positioned at the vertices of a regular 12-gon so that all but one of the vertices are occupied by +1. It is permitted to change the sign of the numbers in any 3 successive vertices of the 12-gon. Is it possible to shift the only -1 sign to the adjacent vertex?
Start from the negative 1 and change the sign for the 3 no.s .so it becomes +1 -1 -1 +1 +1…..+1 9 times .now start changing the sign from the-1 and complete the full polygon this way and we will reach at the answer.
That is negative sign is shifted to the adjacent side opposite to which you started changing signs.