（5-1除以5）乘以5=24
1: 5 × (5 - 1 ÷ 5)2: 5 × (5 - (1 ÷ 5))3: (5 - 1 ÷ 5) × 54: (5 - (1 ÷ 5)) × 5
5*(5-1/5)
