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Old 03-09-2017, 04:17 AM   #1 (permalink)
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Error in my GRE study guide?

It is Xistday in two weeks and I promised myself I would take the GRE on my birthday, but I am not sure I can get ready in-time. I bought the highly-respected eight-volume Manhattan Prep series and got stuck in the third book a while ago. I started over with my girlfriend, who is about to graduate in my major. Somehow we have spent more time watching "Timeless" on Hulu than studying, but we completed most of a chapter tonight, until we got to:

This seemed perfectly clear to me, but the book said:

The powers of 2 [wait, what?] have a repeating pattern of four terms for their units digits: [2, 4, 8, 6]. That means that [for] every fourth term, the pattern repeats. For instance, the 5th term has the same units as the 1st term, because 5 - 1 = 4. So terms that are four terms apart, or multiple of 4 terms apart, will have the same units digit.
The 34th term and the 26th term are 34 - 26 = 8 terms apart. Because 8 is a multiple of 4, the terms will have the same units digit. The two quantities are equal. Incidentally, the units digit of and is 3.
I do not understand how 2n - 1 apparently means . Did I somehow misunderstand this, or is there an error?

Thank you very much for your time! Please enjoy your day!

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Old 03-09-2017, 04:29 AM   #2 (permalink)
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Your quote and the first image are inconsistent. I agree with your interpretation. The quote is factually correct but it does not agree with the scanned image - curious....

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Old 03-09-2017, 06:35 AM   #3 (permalink)
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I was not a math major but it seems accurate to me.

The unit digit (A) is equal in both equations "An = 2n-1". The difference in each equation is the multiple (26) vs (34).
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Old 03-09-2017, 08:39 AM   #4 (permalink)
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^agree with Black Duck. The quote just doesn't relate to the question.


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