1.9+19.9+199.9+1999.9
=(2-0.1)+(20-0.1)+(200-0.1)+(2000-0.1)
=(2+20+200+2000)-0.1*4
=2222-0.4
=2221.6
1.9+19.9+199.9+1999.9=2-0.1+20-0.1+200-0.1+2000-0.1=2222-0.4=2221.6
1.9+19.9+199.9+1999.9
=(2-0.1)+(20-0.1)+(200-0.1)+(2000-0.1)
=(2+20+200+2000)-0.1×4
=贺源备2222-0.4
=禅毁裂卖2221.6
1.9+19.9+199.9+1999.9+0.4-0.4
=2+20+200+2000-0.4
=2222-0.4
=2221.6
2+20+200+2000=2222-0.4=2221.6