1.125+2.125+3.125+4.125……+80.125 =(1+0.125)+(2+0.125)+(3+0.125)+(4+0.125)+……+(80+0.125)=(1+2+3+4+……+80)+0.125×80=(1+80)×80/2+10=81×80/2+10=3240+10=3250