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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:

http://ecomodder.com/forum/attachmen...1&d=1489050165

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 http://ecomodder.com/forum/attachmen...1&d=1489050506 and http://ecomodder.com/forum/attachmen...1&d=1489050654 is 3.

I do not understand how 2n - 1 apparently means http://ecomodder.com/forum/attachmen...1&d=1489050902. Did I somehow misunderstand this, or is there an error?

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

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....

Simon

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).

^agree with Black Duck. The quote just doesn't relate to the question.

I thought that I had asked about another possible error in this same GRE study guide (months later, I am still in the same book!). The other error I remember was something like a 3 in a formula that was supposed to be ^3.

Hilarity did not ensue.

This error was in Chapter five, #17, page 124, explained on 127, of Manhattan Prep GRE Algebra. The image I shared was of my understanding of the problem. The actual problem, taken directly from the book is:

http://ecomodder.com/forum/attachmen...1&d=1502984858

It seems they wrote the problem wrong. On page 115 they explain:
http://ecomodder.com/forum/attachmen...1&d=1502989423

They explain you cannot be expected to multiply this on the GRE, even with a calculator, therefore you must look for a pattern in the powers of three.

I usually skip the lessons and go straight to the problems. Maybe if I read that part I would catch their errors faster. If I have needed to stop and figure out three mistake in the first book, how worth my time is this highest-rated study guide?

The errors are sprinkled in there just to make sure you're paying attention.

Just take the GRE already.

I finally realized Manhattan Prep must have forums, so it would be better to ask there. Sounds obvious, eh?

Why didn't any of you point out that?! :D

Someone asked about this problem and an employee responded "this one is on our errata page in your student center. It should read 2^n, not 2n. Sorry!" https://www.manhattanprep.com/gre/fo...17-t10800.html

They have an entire page of errors?!