12+56+1112+1920+… +98999900=______ .

12+56+1112+1920+… +98999900=______ .

12+56+1112+1920+… +98999900=(1-12)+(1-16)+(1-112)+(1-120)+… +(1-19900)=99-(12+16+112+120+130+… +19900)=99-(1-12+12-13+13-14+14-15+15-16+… +199-1100) = 99 - (1-1100) = 99-1 + 1100 = 98 + 0.01 = 98.01