(7/12-1/2)×3/20 1/80
———————— = ------- = 1/40
13/24÷(7/12+1/2) 1/2
1)7/12 - 1/2 = (7 × 1 - 1 × 6)/12 = 7/12 - 6/12 = 1/12
2)1/12 × 3/20 = 1/80
3)7/12 + 1/2 = (7 × 1 + 1 × 6)/12 = 7/12 + 6/12 = 13/12 = 1 1/12
4)13/24 ÷ 1 1/12 = 13/24 ÷ 13/12 = 13/24 × 12/13 = 1/2
5)1/80 ÷ 1/2 = 1/80 × 2 = 1/40
(1/4+2/3)×6/11 1/2
———————— = ---------- = 2 4/25
(3/4-1/3)×5/9 25/108
1)1/4 + 2/3 =(1 × 3 + 2 × 4)/12 = 3/12 + 8/12 = 11/12
2)11/12 × 6/11 = 1/2
3)3/4 - 1/3 =(3 × 3 - 1 × 4)/12 = 9/12 - 4/12 = 5/12
4)5/12 × 5/9 = 25/108
5)1/2 ÷ 25/108 = 1/2 × 108/25 = 54/25 = 2 4/25