2,4,4,5的24点答案：
1:(2 + 5) × 4 - 4
2:((2 + 5) × 4) - 4
3:(2 × 5 - 4) × 4
4:((2 × 5) - 4) × 4
5:(4 × (2 + 5)) - 4
6:4 × (2 + 5) - 4
7:4 × (2 × 5 - 4)
8:4 × ((2 × 5) - 4)
9:(4 + 4) × (5 - 2)
10:(4 × (5 + 2)) - 4
11:4 × (5 + 2) - 4
12:4 × (5 × 2 - 4)
13:4 × ((5 × 2) - 4)
14:(5 + 2) × 4 - 4
15:((5 + 2) × 4) - 4
16:(5 - 2) × (4 + 4)
17:(5 × 2 - 4) × 4
18:((5 × 2) - 4) × 4
