1.765×213÷27+765×327÷27 =765÷27×(213+327) = 765÷27×540 =765×20 =15300 2.(9999+9997+…+9001)-(1+3+…+999) =(9999-999)+(9997-997)+(9995-995)+……+(9001-1) =9000+9000+…….+9000 (500个9000) =4500000 3.19981999×19991998-19981998×19991999 =(19981998+1)×19991998-19981998×19991999 =19981998×19991998-19981998×19991999+19991998 =19991998-19981998 =10000