5.3×99+5.3-30
=5.3×（99+1）-30
=5.3×100-30
=530-30
=500
2.23×五分之二+2.77÷2.5
=2.23×0.4+2.77×0.4
=0.4×（2.23+2.77）
=0.4×5
=2