4 9 9 12如何等于24
问题描述：
4 9 9 12如何等于24
答
1:4 × (9 + 9 - 12)
2:4 × ((9 + 9) - 12)
3:4 × (9 + (9 - 12))
4:4 × (9 - 12 + 9)
5:4 × ((9 - 12) + 9)
6:4 × (9 - (12 - 9))
7:(4 - 12 ÷ 9) × 9
8:(4 - (12 ÷ 9)) × 9
9:9 × (4 - 12 ÷ 9)
10:9 × (4 - (12 ÷ 9))
11:(9 + 9 - 12) × 4
12:((9 + 9) - 12) × 4
13:(9 + (9 - 12)) × 4
14:(9 - 12 + 9) × 4
15:((9 - 12) + 9) × 4
16:(9 - (12 - 9)) × 4