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The Last Two Digits (Posted on 2013-09-04) Difficulty: 2 of 5
What are the last two digits of (1+5^(2n+1))/6?
Note that n is assumed to be any positive integer.

No Solution Yet Submitted by Danish Ahmed Khan    
Rating: 4.0000 (1 votes)

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Solution answer - spoiler | Comment 1 of 3
 the last two digits  are  21

Proof 1- by induction.

Proof 2- by observing that the odd powers of 5 terminate by 125 or 625.

  Posted by Ady TZIDON on 2013-09-04 10:30:41
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