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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:

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.
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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Old 08-17-2017, 06:20 PM   #5 (permalink)
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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:



It seems they wrote the problem wrong. On page 115 they explain:


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?
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Old 08-17-2017, 07:36 PM   #6 (permalink)
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The errors are sprinkled in there just to make sure you're paying attention.

Just take the GRE already.
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Old 08-18-2017, 12:08 PM   #7 (permalink)
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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?!

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?!

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