算算24点？

如题：1 5 4 2，算算24点

1: (5 - 1) × (4 + 2)

2: (5 - 1 + 2) × 4

3: ((5 - 1) + 2) × 4

4: (5 - (1 - 2)) × 4

5: (5 - 1) × (2 + 4)

6: (5 + 2 - 1) × 4

7: ((5 + 2) - 1) × 4

8: (5 + (2 - 1)) × 4

9: 4 × (5 - 1 + 2)

10: 4 × ((5 - 1) + 2)

11: 4 × (5 - (1 - 2))

12: 4 × (5 + 2 - 1)

13: 4 × ((5 + 2) - 1)

14: 4 × (5 + (2 - 1))

15: 4 × (2 - 1 + 5)

16: 4 × ((2 - 1) + 5)

17: 4 × (2 - (1 - 5))

18: (4 + 2) × (5 - 1)

19: 4 × (2 + 5 - 1)

20: 4 × ((2 + 5) - 1)

21: 4 × (2 + (5 - 1))

22: (2 - 1 + 5) × 4

23: ((2 - 1) + 5) × 4

24: (2 - (1 - 5)) × 4

25: (2 + 5 - 1) × 4

26: ((2 + 5) - 1) × 4

27: (2 + (5 - 1)) × 4

28: (2 + 4) × (5 - 1)

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