a) 4/9 + 2/6 = 4/9 + 1/3 = (43 + 19) / 9*3 = (12 + 9) / 27 = 21 / 27 = 7/9

б) 5 - 3 2/11 = 5 - (3 + 2/11) = 5 - (33/11 + 2/11) = 5 - 35/11 = (55 - 35) / 11 = 20 / 11

в) 3 5/6 - 2 7/9 = (3 - 2) + (5/6 - 7/9) = 1 + (15/18 - 14/18) = 1 + 1/18 = 19/18

г) 7 2/7 + 1 13/14 = (7 + 1) + (2/7 + 13/14) = 8 + (4/14 + 13/14) = 8 + 17/14 = 8 + 1 3/14 = 9 3/14

x - 1 2/7 = 5 3/4
x = 5 3/4 + 1 2/7
x = 20/4 + 3/4 + 7/7 + 2/7
x = 23/4 + 10/7
x = (237 + 104) / 4*7
x = (161 + 40) / 28
x = 201 / 28
x = 100.25