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:
Quote:
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.
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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!