66X21+19X21+85X19怎么简便计算?
问题描述:
66X21+19X21+85X19怎么简便计算?
还有(125+75)X28、36X111+888X8、99X99+199怎么简便计算?
答
66X21+19X21+85X19
=21(66+19)+85X19
=21X85+85X19
=85(21+19)
=85X40
=3600