99²+99÷=99×99+99×1=99×（99+1）=99×100=99004.9-（5分之3+2.4÷2又3分之2）=4.9-（3/5+2.4÷2又2/3）=4.9-[3/5+2.4×(3/8)]=4.9-(3/5+0.9)=4.9-(0.6+0.9)=4.9-0.9-0.6=4-0.6=3.4