Răspuns :
1+3+5+...+21+23+24+25+2+2x2+3x2+...12x2
1+2+3+4+5+25-2-4-6-...-24+2(1+2+...+12)
25x24/2+(-2)(1+2+3+...+12)+2(12x13/2)
25x12+(-2)(12x13/2)+12x13=
25x12-12x13+12x13=25x12=300
1+2+3+4+5+25-2-4-6-...-24+2(1+2+...+12)
25x24/2+(-2)(1+2+3+...+12)+2(12x13/2)
25x12+(-2)(12x13/2)+12x13=
25x12-12x13+12x13=25x12=300