1. 6/21=2/7, 56/63=8/9, 24/36=2/3, 16/80=1/5
2. 5/9=10/18 → 11/18>5/9, 7/18=14/36 5/12=15/36 → 5/12>7/18
3. 23/3=7 2/3, 68/7=9 5/7
4. a=3,3, b=3,3+0,1=3,4, c=3,4-1,3=2,1, P=a+b+c=3,3+3,4+2,1=8,8 (м)
5. ?/?+3/8=10, ?/?=10-3/8, ?/?=9 5/8
?/?-1/10=3/5, ?/?=6/10+1/10, ?/?=7/10