简便计算 ①0.33×19.9 ②4.8×7.8＋78×0.52 ③56.5×9.9＋5.65 ④0.9＋9.9＋99.9＋999.9

0.33*19.9=0.33*20-0.033=6.567
4.8*7.8+78*0.52=4.8*7.8+7.8*5.2=7.8*(4.8+5.2)=78
56.5*9.9+5.65=56.5*(9.9+0.1)=565
0.9+0.1+9.9+0.1+99.9+0.1+999.9+0.1-0.4
=1+10+100+1000-0.4
1110.6

①=0.33×(20-0.1)=6.6-0.033=6.5967
②=7.8(4.8+5.2)=78
③=5.65(99+1)=565
④=(0.9+0.1)+(9.9+0,1)+(99.9+0.1)+(999.9+0.1)-0.4=(1+10+100+1000)-0.4=1111-0.4=1110.6