解：2.7/(1一20%一50%) =2.7/(1一0.20一0.50) =2.7/(1一0.70) =2.7/0.30 =9
1-20%-50%=30%2.7除以30%等于0.81
解: 2.7÷(1-20%-50%)=2.7÷30%=2.7÷0.3=9
