Sequences & Series

Finished AP GP from GMATClub's Math Book. Since we've done AP GP quite extensively in school, concepts are pretty clear to me. It's mostly just formulae otherwise.

Putting this in here because it won't be found everywhere:

"There are some short cuts and concepts that you should know about this topic.

(1) The mean and the medium of any arithmetic sequence is equal to the average of the first and last terms.
(2) The sum of an arthritic sequence is equal to the mean (average) times the number of terms.
(3) The product of n consecutive integers is always divisible by n! So, 4x5x6 (4*5*6=120) is divisible by 3!
(4) If you have an odd number of terms in consecutive set, the sum of those numbers is divisible by the number of terms.
(5) (4) above does not hold true for consecutive sets with an even amount of terms."

An Important Sequence & a CR link

Here's a type of Sequences question I wasn't aware of, till now.

Repeating Patterns

Many times, repeating patterns will yield a remainder question.

The first term of a sequence is  -2 and the second term is 2. Each subsequent odd term is found by adding 2 to the previous term, and each subsequent even terms is found by multiplying the previous term by -1. What is the sum of the first 669 terms?

Clearly, we are not looking to enter all 669 terms and see what the last one is. But, we can do a few and check out the pattern.
n = 1, = -2
n = 2, = 2
n = 3, = 4
n = 4, = -4
n = 5, = -2
n = 6, = 2
Since we can see that the pattern will repeat every 4 terms, we can solve for the remainder after dividing 669/4. Since 4 goes into 668 evenly, we know that the value will be equivalent to that of the first term, which = -2.

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Also discovered a whole host of useful GMAT CR articles on BTG. Read the first two (in chronological order) and found them pretty useful. Even assumptions are of two types: sufficient and necessary! And the question type (by a subtle change in wording) can change the answer! Damn. Those 2 are definite re-read material.

Update/Day 9

Sorry for not updating earlier!

Day 6: MGMAT FCs - Word Translations (WT)
Day 7: MGMAT FCs - EIVs
Day 8: Theory (only formulas) for P&C, Interest (SI & CI), Sequences (AP,GP)
Day 9 (TODAY, 13th Oct): Just gave a 40 minute Math Diagnostic on MGMAT site. Was good! But questions were of 200-500 level. I got 19/20 questions right. The 1 I got wrong was silly - was a remainders question, and I should've just used common sense instead of trying to fit in a formula. Anyway, yay!

If I'm not too tired in the evening, I'll try doing some more from IMS BRM material on P&C...let's see.
Btw, I'm going to pay for GMAT by myself! :-) (earlier, my parents were going to)
I will be done with it by Dec end, and then...I'm going to apply to BCG, Bain & Co, and other consultancy firms in that league. I want to work there!!! I *will* work there.
GMAT studying, as you can see, is going at a slow pace, but it's consistent atleast. I want to try giving the OG11 diagnostic by this weekend (3-day weekend coming up! Yay Diwali!)

I'm off to try exercising a little before I go to office.

Happy studying!