Question

41.2×8.1+21×1.25+53.7×1.9怎么简便？

要快啊！这个明天就要上交了！

Answer 1

41.2×8.1+21×1.25+53.7×1.9

=41.2×(10-1.9)+53.7×1.9+21×1.25

=412+1.9×(53.7-41.2)+21×1.25

=412+(19+21)×1.25

=412+40×1.25

=412+50

=462

乘法的计算法则：

数位对齐，从右边起，依次用第二个因数每位上的数去乘第一个因数，乘到哪一位，得数的末尾就和第二个因数的哪一位对齐。

凡是被乘数的各位数遇到7、8、9时，其方法为：

是9：本位减补数-次，下位加补数一次。

被乘数是8：本位减补数一次，下位加补数二次。

是7：本位减补数一次，下位加补数三次。

例如：987x879=867573（879的补数是121）算序：被乘数个位7的本位减121，下位加363得98-6153。被乘数-+位8的本位减121，下位加242得9-76473。被乘数百位9的本位减121，下位加121得867573（积）。

Answer 2

41.2×8.1+21×1.25+53.7×1.9
=41.2×(10-1.9)+53.7×1.9+21×1.25
=412+1.9×(53.7-41.2)+21×1.25
=412+(19+21)×1.25
=412+40×1.25
=412+50
=462

Answer 3

41.2×8.1+21×1.25+53.7×1.9
=41.2×(10-1.9)+53.7×1.9+21×1.25
=412-41.2X1.9+53.7×1.9+21×1.25
=412+1.9×(53.7-41.2)+21×1.25
=412+1.9×12.5+21×1.25
=412+(19+21)×1.25
=412+40×1.25
=412+50
=462