56.5X9.9十5.65X1=56.5X9.9十56.5X0.1=56.5X(9.9十0.1)=56.5X10=565
56.5X9.9十5.65X1=56.5X9.9十56.5X0.1=56.5X(9.9+0.1)=56.5X10=565
56.5X9.9十5.65X1=5.65*99+5.65*1=5.65*(99+1)=5.65*100=565
9.9写成10-0.1