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Re: What is the unit digit of A=2+2^2+2^3+...+2^10?
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20 Dec 2016, 05:27

Fisrt, find the cyclicity of 2 = 4 (2;4;8;6) Second, find number of cycles Since last number of set contains 2^20, so we have 20 as greatest power. 20 is a multiple of 4, 20/4=5. So we have 5 full cycles. Lastly, we just need to sum up all possible values of powers 2+4+8+6=20, thus 0 is the unit digit, answer A. Solved in 36 sec.

Re: What is the unit digit of A=2+2^2+2^3+...+2^10?
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06 Feb 2019, 18:41

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