4: ① 1/3 2/3
② 1/9 2/9
5: ① 1/6
② 2/9 9/2
③ 2/5 5/2
6: ① 50÷6=8…… 2
8×3+2=26
26÷50=26/50
② 8×2=16
16÷50=16/50
③ 8÷50=8/50