Find the rth term of this sequence

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Given a sequence:
3,33,333,3333,..........
Find the rth term of this sequence.

This sequence does not belong to Geometry Progression or Arithmetic Progression. From what I know, rth term is equals to (r-1)*10 +3.

But how do I solve this problem?
 
Harmony said:
This sequence does not belong to Geometry Progression or Arithmetic Progression. From what I know, rth term is equals to (r-1)*10 +3.
Hint:
[tex]\sum\limits_{k = 0}^n {r^k } = \frac{{1 - r^{n + 1} }}{{1 - r}}[/tex]

The rth term of your sequence is just (10r-1)/3 :smile:
 

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