The number 1.111111 . . . itself is the sum of the infinite geometric progression with the first term a= 1 and the common ratio 0.1, so 1.111111 . . . == . Next, the given sum is the sum of the geometric progression with the first term and the common ratio of 0.1, so this sum is equal to = = 1/0.81. Answer. The sum under the question is equal to , or .