Дробь к общему знаменателю 2/15 и5/12,5\12и7/8,7/33и3/77,2/55и5/22,1/72и1/56,1/42и1/54,9/35и11/42

2/15  и 5/12
2*4/(15*4) и 5*5/(12*5)
8/60 и 25/60

5/12 и 7/8
5*2/(12*2) и 7*3/(8*3)
10/24 и 21/24

7/33 и 3/77
7*7/(33*7) и 3*7/(77*3)
49/231 и 21/231

2/55 и 5/22
2*2/(55*2) и 5*5/(22*5)
4/110 и 25/110

1/72 и 1/56
1*7/(8*9*7) и 1*9/(7*8*9)
7/504 и 9/504

1/42 и 1/54
1*9/(7*6*9) и 1*7/(7*6*9)
9/378 и 7/378

9/35 и  11/42
9*6/(7*5*6) и 11*5/(7*5*6)
54/210 и 55/210