13,8,3,2的24点答案：
1:(13 + 3) × 2 - 8
2:((13 + 3) × 2) - 8
3:(3 + 13) × 2 - 8
4:((3 + 13) × 2) - 8
5:(2 × (13 + 3)) - 8
6:2 × (13 + 3) - 8
7:(2 × (3 + 13)) - 8
8:2 × (3 + 13) - 8