Răspuns:
Explicație pas cu pas:
21/63 = 1/3
201/603 = 1/3
2001/6003 = 1/3
20001/60003 = 1/3
............
20...01/60...03 = 1/3
A = 1/3 + 1/3 + 1/3 + 1/3 + .... + 1/3 = 90*1/3 = 30
