41*101=41*(100+1)=41*100+41*1=4100+41=4141
907*99+907=907*(99+1)=907*100=90700
56*99=56*(100-1)=56*100-56=5600-56=5544
4.05-2.8-0.7=4.05-(2.8+0.7)=4.05-3.5=0.55