=7.28x(3.1+7.9-1) =7.28x10 =72.8
7.28_2.28×1.5用简便方法计算 =7.28×（1-1.5） =7.28×（-0.5） =3.64
7.28减2.28乘1.5用简便方法计算 =7.28-2.28-2.28x0.5 =5-1.14 =3.86
用简便方法计算 7.28-2.28×1.5 =7.28-2.28-2.28x0.5 =5-1.14 =3.86
7.28-（1.28+0.25） =7.28-1.28-0.25 =6-0.25 =5.75
7.28减2.28乘1.5简便算 7.28减2.28乘1.5 =7.28-3.42 =3.86 直接计算