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.
答
(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.
答案解析:(1)两次运用乘法分配律简算;
(2)先把888×8分解成111×64,再运用乘法分配律简算;
(3)先把99分解成100-1,再运用乘法分配律简算.
考试点:运算定律与简便运算.
知识点:乘法分配律是最常用的简便运算的方法,要熟练掌握,灵活运用.