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I don't know where I got wrong with this problem. My answer is different from the answer sheet. To solve this problem, I used geometric sequence as $a, ar, ar^2 ..., ar^9$ and arithmetic sequence as $0, b, 2b,..., 9b$. Then I used the following equations to find a, r, and b, and from there I found the sum of the first 10 terms of the third sequence. $a+0=1$, $ar+b=1$, $ar^2+2b=2$

Given a geometric sequence with the first term a and common ratio r, where both a and r not equal to 0, and an arithmetic sequence with the first term 0, a third sequence 1,1,2... is formed by adding the corresponding terms of the 2 given sequences. Find the sum of the first 10 terms of the third sequence.

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  • $\begingroup$ @labbhattacharjee That should be $r^2+2(1-r)=2$. There are two solutions. $\endgroup$ – Théophile May 21 '16 at 13:48
  • $\begingroup$ Thanks. I know where I made a mistake now. Since the problem said that r is not zero, r should be 2. $\endgroup$ – user321527 May 21 '16 at 13:51
  • $\begingroup$ @FSK if you solved your problem, you should describe solution in answer, or delete question (if solution won't be helpful for others). $\endgroup$ – Tacet May 21 '16 at 14:38

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