（71.2-71.2×0.9）÷0.25=71.2×（1-0.9）÷0.25=71.2×0.1÷1/4=7.12×4=28.48
（71.2-71.2×0.9）÷0.25＝71.2×（1-0.9）÷1/4＝71.2×0.1×4＝7.12×4＝28.48
