2,7,8,9的24点答案：1:(2 × (7 + 9)) - 82:2 × (7 + 9) - 83:(2 × (9 + 7)) - 84:2 × (9 + 7) - 85:(7 + 9) × 2 - 86:((7 + 9) × 2) - 87:(9 + 7) × 2 - 88:((9 + 7) × 2) - 8