[(7/8 - 1/4) × 2/5] ÷ 5/9
原式 = [5/8 × 2/5] × 9/5
= 1/4 × 9/5
= 9/20
5/17 ÷ 9 + 1/9 × 12/17
原式 = 5/17 × 1/9 + 1/9 × 12/17
= (5/17 + 12/17) × 1/9
= 1 × 1/9
= 1/9
3/4 + 1/6 - 3/8
原式 = (18+4-9)/24
= 13/24
(1/5 + 1/3 - 1/7) × 10.5
原式 = 1/5 × 10.5 + 1/3 × 10.5 - 1/7 × 10.5
= 2.1 + 3.5 - 1.5
= 5.6 - 1.5
= 4.1
36 ÷ 0.8 ÷ 1.25
原式 = 36 ÷ (0.8 × 1.25)
= 36 ÷ 1
= 36