用简便方法计算下面各题. (1)66×21+19×21+85×19 (2)36×111+888×8 (3)99×99+199.

问题描述:

用简便方法计算下面各题.
(1)66×21+19×21+85×19
(2)36×111+888×8
(3)99×99+199.

(1)66×21+19×21+85×19,
=(66+19)×21+85×19,
=85×21+85×19,
=85×(21+19),
=85×40,
=3400;
(2)36×111+888×8,
=36×111+111×8×8,
=36×111+111×64,
=(36+64)×111,
=100×111,
=11100;
(3)99×99+199,
=99×(100-1)+199,
=99×100-99×1+199,
=9900-99+199,
=9900+(199-99),
=9900+100,
=10000.