a) 0,(3) = 3 / 9 = 1 / 3
0,1(6) = ( 16 - 1) / 90 = 15 / 90 = 1 / 6
1 / 3 × 1 / 6 = 1 / 18
b)
0,25 = 25 / 100 = 1 / 4
1 / 4 × 4 / 5 = 1 / 5
c)
0,(13) = 13 / 99
13 / 99 × 10 / 39 = 10 / 99 × 3 = 10 / 297
d)
1,2(9) = ( 129 - 12) / 90 = 117 / 90 = 39 / 30 = 13 / 10
13 / 10 × 10 / 3 = 13 / 3 = 4,(3)