3.8X2.5X7.2 =[(4-0.2)X2.5]X7.2 =[10-0.5]X7.2 =72-3.6 =68.4 5.09X6.4+3.6X5.09 =5.09X(6.4+3.6) =5.09X10 =50.9 12.8X10.1 =12.8X(10+0.1) =128+1.28 =129.28 望采纳!
