第 4 关

括号的魔法：给运算发“插队券”

5 × 5 + 15 ÷ 3 = 50

9 + 6 ÷ 3 + 6 = 11

15 + 20 ÷ 2 + 3 = 7

2 + 8 × 3 + 1 – 5 = 35

5 × (5 + 15 ÷ 3) = 50 ← 5 × 10

(9 + 6) ÷ 3 + 6 = 11 ← 5 + 6

(15 + 20) ÷ (2 + 3) = 7 ← 35 ÷ 5

(2 + 8) × (3 + 1) – 5 = 35 ← 40 – 5

等号两边各一对： 1 ÷ 2 + 3 – 4 + 5 = 5 × 4 – 3 + 2 – 1

1 ÷ (2 + 3 – 4) + 5 = 5 × (4 – 3) + 2 – 1 ← 6 = 6

技巧：先看得数，想一想“谁 × 谁”“谁 ÷ 谁”能得到它，就把括号加在那里