Dear jabgars,
I'm happy to help.

First of all, here's a free IR ebook you may find helpful:
http://magoosh.com/gmat/2012/gmat-integ ... ing-ebook/

One important skill on IR is estimation --- see:
http://magoosh.com/gmat/2012/the-power- ... mat-quant/

Question #1
At the end of September:
Biofirm is just less than 50 --- we could say 49 or 50
Argent is about 15
Compuwin is about 33
Notice --- exact values are not as important, because we are going to estimate.
B + A is about 65 --- that's essentially double what C is. If thing #1 is double thing #2, then thing #1 is 100% greater than thing #2. Therefore, (A + B) are about 100% greater than C. Answer = (D)

Question #2
Let's look for some low-hanging fruit here ----
(A) July - hmmm B has a big jump, and A & C have little drops, hmmm
(B) August - hmmm, this looks promising, because C stays level, the the rise in B seems equal to the drop in A
(C) October - NO WAY -- huge drops in B & C, only a modest rise in A
(D) November - the drop in C seems equivalent to the rise in A, but B also rises --- a net gain --- NO WAY
(E) December - NO WAY - gigantic rise in A and small rise in C are no way offset by small drop in B.

Without any calculations, with purely visual inspection, I can see that (C) & (D) & (E) are out. Now, I have to look more careful at (A) & (B). In (A) July, the gains in A & C are small, even combined --- it seems the rise in B is enough for a net gain. Meanwhile, in (B) August, the the rise in B seems equal to the drop in A, and C stays flat, so that really looks like zero change.
Answer = (B)

Are you familiar with the phrase, "A picture is worth a thousand words"? That's the principle of a graph --- that's why mathematicians & data wonks love graphs. We can convey so much information visual, and one of the big ideas of working with graphs on the GMAT is not to get sucked into numerical calculations each time, but to process the graphs visually.

Does all this make sense?
Mike
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Dear Mike,
Thank you for the solution,
I have a question related to part 1 .

When we were asked to find the " By how much % Compuwin firms share value exceeded the value of Biofirm and Ardent firm share value"
what I did was in a way calculate the % increase
[(65 - 33)/ 65 ] * 100
= approx 50%

hence I chose C.
Why is this wrong? What is the error in my understanding?
Thank you.
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Dear stne,

I'm happy to respond.

My friend, you got the comparison reversed, and you even wrote it in the wrong order. Pay extremely close attention to wording: in math, the words have to be interpreted as precisely as the numbers. Here's the exact wording of the text of the question:
At the end of September, the combined share price of Ardent stock and Biofirm stock exceeded the share price of Compuwin stock by approximately ...
In the question "by how what percent does X exceed Y?", we have to put Y in the denominator because that's the baseline to which the comparison will be made. If we reverse the roles of X & Y, as you did, we get a very different answer.

In your calculation, the price of a share of Compuwin, 33, should be in the denominator. Because you swapped the order, you have the correct numerator and the wrong denominator.

Does all this make sense, my friend?
Mike
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