9 + 9 - 9 ÷（√9 × √9）= 17
9 - 9 + √9 + √9 + √9 = 18
9 ÷ 9 + √9 + √9 + √9 = 19
9 + 9 + (√9 + √9) ÷ √9 = 20小学里没有根号(9 × 9 - 9) ÷ 9 + 9 = 17(99 ÷ 9 - 9) × 9 = 18(9 × 9 + 9) ÷ 9 + 9 = 19(9 + 9) ÷ 9 + 9 + 9 =20