Try this solution:
1. Note, that 9*0.1=0.9; 0.9*0.1=0.09; 0.09*0.1=0.009, etc.
It means, the gives series is geometric sequence, where a₁=9, q=0.1.
2. Using a₁=9 and q=0,1 it is possible to calculate the sum of this sequence:
answer: 10
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