Question

13-12+11+10-9+8-7-6+5-4+3+2-1

 

Answer 1

\(13-12+11+10-9+8-7-6+5-4+3+2-1\\ =13-\left(12+1\right)-\left(11+2\right)-\left(10+3\right)-\left(9+4\right)-\left(8+5\right)+\left(7+6\right)\\ =13-13-13-13-13-13+13\\ =0+13\\ =13\)

Answer 2

\(13-12+11+10-9+8-7-6+5-4+3+2-1\)

\(=1+11+10-9+8-7-6+5-4+3+2-1\)

\(=12+10-9+8-7-6+5-4+3+2-1\)

\(=22-9+8-7-6+5-4+3+2-1\)

\(=13+8-7-6+5-4+3+2-1\)

\(=21-7-6+5-4+3+2-1\)

\(=14-6+5-4+3+2-1\)

\(=8+5-4+3+2-1\)

\(=13-4+3+2-1\)

\(=9+3+2-1\)

\(=12+2-1\)

\(=14-1\)

\(=13\)