16.5 ÷ (16.5X0.4)= 16.5 ÷ 16.5 ÷ 0.4= 1 ÷ 0.4= 2.5
16.5÷16.5X0.4=1×0.4=0.4
改写成16.5÷16.5÷0.4=1÷0.4=2.5