Дроби к наименьшему общему знаменателю : 1/6 и 1/9. 1/30 и 1/50. 1/24 и 1/120. 3/40 и 7/25. 5/16 и 5/12 . 5/121 и 8/99. 1/51 и 1/68. 15/98 и 13/72.

1/6 и 1/9 = 3/18 и 2/18
18 : 6 = 3 - доп.множ. к 1/6 = (1*3)/(6*3) = 3/18
18 : 9 = 2 - доп.множ. к 1/9 = (1*2)/(9*2) = 2/18

1/30 и 1/50 = 5/150 и 3/150
150 : 30 = 5 - доп.множ. к 1/30 = (1*5)/(30*5) = 5/150
150 : 50 = 3 - доп.множ. к 1/50 = (1*3)/(50*3) = 3/150

1/24 и 1/120 = 5/120 и 1/120
120 : 24 = 5 - доп.множ. к 1/24 = (1*5)/(24*5) = 5/120

3/40 и 7/25 = 15/200 и 56/200
200 : 40 = 5 - доп.множ. к 3/40 = (3*5)/(40*5) = 15/200
200 : 25 = 8 - доп.множ. к 7/25 = (7*8)/(25*8) = 56/200

5/16 и 5/12 = 15/48 и 20/48
48 : 16 = 3 - доп.множ. к 5/16 = (5*3)/(16*3) = 15/48
48 : 12 = 4 - доп.множ. к 5/12 = (5*4)/(12*4) = 20/48

5/121 и 8/99 = 45/1089 и 88/1089
1089 : 121 = 9 - доп.множ. к 5/121 = (5*9)/(121*9) = 45/1089
1089 : 99 = 11 - доп.множ. к 8/99 = (8*11)/(99*11) = 88/1089 

1/51 и 1/68 = 4/204 и 3/204
204 : 51 = 4 - доп.множ. к 1/51 = (1*4)/(51*4) = 4/204
204 : 68 = 3 - доп.множ. к 1/68 = (1*3)/(68*3) = 3/204

15/98 и 13/72 = 540/3528 и 637/3528
3528 : 98 = 36 - доп.множ. к 15/98 = (15*36)/(98*36) = 540/3528
3528 : 72 = 49 - доп.множ. к 13/72 = (13*49)/(72*49) = 637/3528