40×20=(4×10)×(2×10)=(4×2)×(10×10)=8×100=800
0.4×0.2=(4×0.1)×(2×0.1)=( × )×( × )= ×
=(4× )×(2× )=( × )×( × )= ×
8.1÷0.03= +3= ×= ﹣=
×= 134﹣18= ×0÷3= 7.45+8.55=