用简单算法算术9.99×9.99+19.99= 4.8÷0.6+4.8÷0.4= （11.2+1.48÷3.7)÷0.4= (0.8+1÷1.25)×12.5=

9.99×9.99+19.99=9.99×10-0.0999+20-0.01=99.9+20-0.1099=119.9-0.1099=119.8-0.0099=119.7901

4.8÷0.6+4.8÷0.4=4.8×10/6+4.8×10/4=4.8×(10/6+10/4)=4.8×50/12=240/12=20

（11.2+1.48÷3.7)÷0.4=（11.2+1.48×10/37)÷0.4=(11.2+14.8/37)÷0.4=(11.2+0.4)×2.5=11.2×2.5+1=11.2×2+11.2/2+1=22.4+5.6+1=29

(0.8+1÷1.25)×12.5=(0.8+4/5)×12.5=0.8×12.5+0.8×12.5=10+10=20

1. (10-0.01)(10-0.01)+20-0.01
=10^2+2*10*0.01+0.01^2+20-0.01
=100+0.2+0.0001+20-0.01
=120.1999

2. 4.8÷0.6+4.8÷0.4
=4.8*3/5+4.8*2/5
=4.8(3/5+2/5)
=4.8×1
=4.8

3.（11.2+1.48÷3.7)÷0.4
=（11.2+1.48×10/37)÷0.4
=(11.2+14.8/37)÷0.4=(11.2+0.4)×2.5=11.2×2.5+1
=11.2×2+11.2/2+1
=22.4+5.6+1
=29

4.(0.8+1÷1.25)×12.5
=0.8×12.5+1÷1.25×12.5
=10+10
=20