42×125 =7x(8x125)=7x1000=7000
473+79-63 =400+73+79-63=400+79+(73-63)=489
5×999+5+99×7+7+3×9+3+9
=5x(999+1)+7x(99+1)+3x(9+1)+9
=5000+700+30+9
=5739我问问你，7×8得多少？我看你得好好背背乘法口诀了把.呃..sorry..42×125 =5.25x(8x125)=5.25x1000=5250