24点题目：使用数字 1 7 8 9，利用加减乘除、括号算出24。数字顺序可以任意调换，下面列出所有可行算式。
本题共有33个解（使用交换律变换后算一个解）,
难度系数是3星
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中等偏易24点题目
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| 序号 |
题目：1,7,8,9 |
| 1 |
((9 + 7) + 8) × 1 |
| 2 |
((9 + 8) + 7) × 1 |
| 3 |
((8 + 7) + 9) × 1 |
| 4 |
((8 × 1) + 7) + 9 |
| 5 |
((9 + 8) × 1) + 7 |
| 6 |
((9 × 1) + 7) + 8 |
| 7 |
((8 + 7) × 1) + 9 |
| 8 |
((9 + 7) × 1) + 8 |
| 9 |
((9 × 1) + 8) + 7 |
| 10 |
(8 + (7 × 1)) + 9 |
| 11 |
(9 + 7) + (8 × 1) |
| 12 |
(9 + (8 × 1)) + 7 |
| 13 |
(8 + 7) + (9 × 1) |
| 14 |
(9 + (7 × 1)) + 8 |
| 15 |
(9 + 8) + (7 × 1) |
| 16 |
8 × ((9 − 7) + 1) |
| 17 |
8 × (9 − (7 − 1)) |
| 18 |
8 × ((9 + 1) − 7) |
| 19 |
((9 + 7) + 8) ÷ 1 |
| 20 |
((9 ÷ 1) + 7) + 8 |
| 21 |
((9 + 8) ÷ 1) + 7 |
| 22 |
((9 + 8) + 7) ÷ 1 |
| 23 |
((9 + 7) ÷ 1) + 8 |
| 24 |
((8 ÷ 1) + 7) + 9 |
| 25 |
((8 + 7) + 9) ÷ 1 |
| 26 |
((9 ÷ 1) + 8) + 7 |
| 27 |
((8 + 7) ÷ 1) + 9 |
| 28 |
(9 + 8) + (7 ÷ 1) |
| 29 |
(8 + 7) + (9 ÷ 1) |
| 30 |
(9 + (7 ÷ 1)) + 8 |
| 31 |
(9 + (8 ÷ 1)) + 7 |
| 32 |
(9 + 7) + (8 ÷ 1) |
| 33 |
(8 + (7 ÷ 1)) + 9 |