Question

小学四年级数学黄冈小状元第23页培优作业：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

Answer 1

1. 66x21+19x21+85x19
= 21x2+19x2+66x85
=(22+38)+5610
=60+5610=5670

Answer 2

（1）66×21+19×21+85×19 =21×（66+19）+85×19 =21×85+85×19=85×（21+19）=85×40=3400

（2）36×111+888×8 =36×111+8×111×8=111×(36+64)=11100
（3）99×99+199=99×(100-1)+199=9900-99+199=10000

Answer 3

(1)66x21+19x21+85x19 (2) 36x111+888x8 (3) 99x99+199
=21x(66+19)+85x19 =36x111+111x8x8 =100x99+199-99
=21x85+85x19 =111x(36+64) =9900+100
=85x40 =111x100 =10000
=3400 =11100

Answer 4

（1）=21×（66+19+85）+（19-12）×85
=21×170+7×85
=21×170+3.5×170
=24.5×170
=4165
(2) =36×111+111×8×8
=111×(36+64)
=111×100
=11100
(3) =99×99+99+100
=99×(99+1)+100
=99×100+100
=(99+1)×100
=10000

Answer 5

（1）66×21+19×21+85×19 =21×（66+19）+85×19 =21×85+85×19=85×（21+19）=85×40=3400

（2）36×111+888×8 =36×111+8×111×8=111×(36+64)=11100
（3）99×99+199=99×(100-1)+199=9900-99+199=10000