1/3 – 1/6 =… 3/21 – 1/7 =… 1/6 – 1/9 =…

1. 1/3 – 1/6 = 2/6 – 1/6 = 1/6
2. 3/21 – 1/7 = 3/21 – 3/21 = 0
3. 1/6 – 1/9 = 3/18 – 2/18 = 1/18

(sorry ya kalah salah)