\(T\text{ổng}.ba.s\text{ố}.l\text{à}:290\times2=580\\ S\text{ố}.th\text{ứ}.nh\text{ất}.l\text{à}:\left(580+30\right):2=610:2=305\\ S\text{ố}.th\text{ứ}.hai.l\text{à}:305-30=275\\ S\text{ố}.th\text{ứ}.3.l\text{à}:275-30=245\)ta xếp đc như sau:245;275;305
