Ok, no...I'm back!

Remember the last post? Scratch that. There will never be a "right time" to study for GMAT. This IS the right time. Just going to buy MGMAT's SC guide. I have 4 days to go through it once, since work starts 4th Jan. :-) Yey! I'm so glad to be hitting my books again! :-)

Long Break

Hi,
I'm changing jobs. And this new one is expected to keep me super busy. But, I'm excited about it because it's something I've wanted to do for sometime now! It also means I will not be studying for GMAT anymore. I'll get back to it probably after a year or so. Or sooner, or later. Depending on how things go. It sucks not being able to use my GMAT books anymore. OG12 hasn't even been touched yet. Hmmm...
Well, I hope I do get back to it soon enough. Let's see how work goes.

Happy studying till then!

Manhattan GMAT Sentence Correction Guide 4th ed in New Delhi

I have been frantically looking for this as I have lots of free time in the coming week. I called up Om Book Shop and guess what? They have it! I still don't have it in my hands, so I cannot confirm. Will confirm by tonight. Omg. I really hope they actually have it!!! Edit: They DO have it. :-)

And since my GMAT date is getting closer, I think the following post has done me some good. Def starting OG12 this week.
http://gmatclub.com/forum/760-in-5-weeks-you-can-do-it-87741.html

CP #8

Here is the question I didn't get in my last PR test: 

Q. A man chooses an outfit from 3 different shirts, 2 different pairs of shoes, and 3 different pants. If he randomly selects 1 shirt, 1 pair of shoes, and 1 pair of pants each morning for 3 days, what is the probability that he wears the same pair of shoes each day, but that no other piece of clothing is repeated?

a) (1/3)^6 x (1/2)^3

b) (1/3)^6 x (1/2)

c) (1/3)^4

d) (1/3)^2 x (1/2)

e) (1/3)^2 x 5 

Solution:

I came up with an extremely simplified, but slightly longer solution, mainly because I didn't "get" the solutions posted completely. The method is still the same, but this is my explanation for why it is the way it is:

Suppose the shirts are - Y (yellow), G (green), W (white)

The shoes are - T (teal), V (violet)

And the pants are - R (red), L (lemon), A (aqua)

Yes, the man has a horrible sense of fashion. Let's call him Punk! 

Note: My explanation is based on a simple rule my math tutor taught me in school -- 'and' always translates into 'x' (multiplication) and 'or' always becomes '+' (addition). 

Now, the probability of him picking up a particular shirt, say Y = 1/3

This is the probability of each shirt, and so P(Y) = P(G) = P(W) = 1/3

Same for pants i.e. P(R) = P(L) = P(A) = 1/3
For shoes = P(T) = P(V) = 1/2

Day 1:

Mr. Punk can choose an outfit (Shirt & Shoes & Pants) by combining any of the above items.

P (choosing a shirt) = P(Y) or P(G) or P(W)

Similarly,

P (choosing a pair of shoes) = P(T) or P(V)

P (choosing a pair of pants) = P(R) or P(L) or P(A)

One of each item has to be picked up at the same time, so we will multiply the above. The equation is:

P (1Shirt, 1Shoe, 1Pant) = [ P(Y) + P(G) + P(W) ] x [ P(T) + P(V) ] x [ P(R) + P(L) + P(A) ]

The RHS (right hand side of the equation) can be put in words:

He must have picked either the Y 'or' G 'or' W shirt AND a T 'or' V shoe AND a R 'or' L 'or' A pant. I simply converted the 'or' to + & the AND to x.

P (1Shirt, 1Shoe, 1Pant) = (1/3 + 1/3 + 1/3) x (1/2 + 1/2) x (1/3 + 1/3 + 1/3)

= 3/3 x 2/2 x 3/3

= 1.

Most people can derive this by common sense, since the probability of him choosing n combination of outfits has to be 1, because although the combos may be different, the probability of him choosing 1 piece of clothing from each item is a 100% (he will not walk out half-naked!). Anyway, common sense is not so common, so I needed to explain this to myself.

Day 2:

Let us suppose that Mr. Punk picked out Y shirt, T shoes & R pants.

Here is where I had made a mistake. I had assumed that the items he could choose his day 2 outfits from had reduced. In reality, he once again had the same choice from 3 shirts, 2 shoes & 3 pants (yes, he doesn't send his clothes to the laundry after wearing them just once!)

Now the limitation of him choosing a different shirt & pants, and the same shoes, is what we have to look for i.e. what is the probability of that happening by chance, not by him deliberately choosing only from the remaining 2 shirts, etc.

The equation for day 2 will look like this:

P (1Shirt, 1Shoe, 1Pant) = [ P(G) + P(W) ] x [ P(T) ] x [ P(L) + P(A) ]

(since he's already worn the Y & R, and he has to choose only T again.)

P (1Shirt, 1Shoe, 1Pant) = (1/3 + 1/3) x (1/2) x (1/3 + 1/3)

= 2/3 x 1/2 x 2/3

= 2/9

Day 3:

Mr. Punk wore G shirt, T shoes & L pants on day 2.

For day 3, what is the probability of him wearing W shirt, T shoes & A pants?

P (W Shirt, T Shoe, A Pant) = P(W) x P(T) x P(A)

= 1/3 x 1/2 x 1/3

= 1/18 

Multiplying the final blue equations for days 1 AND 2 AND 3 (remember, AND => multiplication),

P (different shirt, pants, and same shoes, on the 3 days) = 1 x 2/9 x 1/18

= 1/81 or (1/3)^4 

PS. I've kept my earlier thoughts on the question...just in case I need them some day:

I made one MAIN mistake. I was thinking he had to choose a particular outfit, and I calculated the probability of that. That's why I was getting answer B I think. Anyway, after reading a couple of solutions posted on the web, I figured it out. We're looking for the probability of him not repeating that same outfit, and there IS replacement here! I had assumed that once shirt#1 is gone, he's left to choose between any of the remaining 2, when in fact he still has his 3 shirts to choose from, but now he can actually pick any 1 of the 2. This explanation is beginning to suck.

After some thought, I finally understood the solution. The solutions I found on GMAT forums helped.

Collective nouns

An excellent video tutorial on collective nouns by a Knewton guy on BTG.



I will definitely need to look at it a couple of times to get those damn rules literally inscribed on my brain.

Flashcard Advice

Here's my first real piece of GMAT advice I posted on a GMAT Club thread MGMAT Math Study Tips? (thread created by user "ant700gmat")

The query:

"Hey Guys,
I’m currently in the process of studying for the GMAT quant section using the MGMAT guides.
Do you have any tips on how to better remember the concepts/rules/formulas in the guides? Any advice would be helpful..
Thanks!"

My reply:

In one word, FLASHCARDS.

While you're going through a chapter, write down notes on concepts, formulas, etc. that are new to you, or you feel you need to commit to memory cos you may forget it.
Make flashcards out of these notes at the end of the chapter, to make review easier, and also to have a handy set of notes to refer to on the move.

A tip on the content of flashcards:
Convert the concept into a question, and put the answer on the back side of the flashcard. For example, if you've just learnt that 1 is not a prime number...put down "List the first 10 prime numbers" as a question, and you'll automatically cover the concept you were actually trying to recall. The reason I feel this is a better way is because sometimes, you tend to remember exactly what was written behind your flashcard, and well...it isn't really too helpful. By making a question out of it, you're APPLYING the formula/concept in a question format, which is a much better way to learn for the GMAT! Well, according to me.

The same goes for a formula. If you want to learn the area of a square, don't write "what is the formula for the area of a square?" Instead, make a question out of it. Eg. "If one side of a square is equal to 2 cms, what is the area of the square?" It's even better if you can make a question where you first have to figure out that the quadrilateral is actually a square (it's not given), and so once you figure out it's a square, you use the formula of a square's area. It will help you remember a lot of concepts, and you can have a lot of fun with it and come up with any number of questions on your own!

And yes, it is a time-consuming process (the last few flashcards I made have actually started to look like boring "what's the formula for simple interest?")...but I think it might be worth it.

Day 29-30

Day 29:
Qs. 1-19 from PR VB3. Timed: 1.8 min/qs.

Day 30:
Qs. 20-26 from PR VB3. Timed. Done now.

Review & error log entry coming soon...

Day 28

Here is the PR Assessment Summary:

QUANT

Category	R	W	U	% Correct
Problem Solving	19	3	0	86%
PS Math Definitions	1	0	0	100%
PS Frac/Dec/Percent	3	0	0	100%
PS Exponents/Roots	1	0	0	100%
PS Ratios/Proprtns	2	0	0	100%
PS Avgs/Rates/Stats	2	0	0	100%
PS Probablility	0	1	0	0%
PS Plugging In	5	1	0	83%
PS PITA	2	1	0	67%
PS Estimation	1	0	0	100%
PS Geometry	2	0	0	100%
Data Sufficiency	12	3	0	80%
DS Math Definitions	2	1	0	67%
DS Frac/Dec/Percent	1	0	0	100%
DS Ratios/Proprtns	1	1	0	50%
DS Avgs/Rates/Stats	1	0	0	100%
DS Eqtns/Inequals	2	1	0	67%
DS Simul Eqtns	1	0	0	100%
DS Geometry	1	0	0	100%
DS Yes/No	3	0	0	100%

Most of my Math errors were caused by not reading the question/statements/answer choices carefully! I used the wrong formula in one place (silly!!! I knew the right formula but blanked out during the exam), and there was one concept error. I didn't realise that if you try to put a cylinder in a cuboid, the maximum diameter of the cylinder can NEVER be equivalent to the longest side of the cuboid. This is because even the floor of the cuboid would have one side which is NOT the longest side. And therefore, the diameter of that cylinder can only be equal to the second longest side of the cuboid, and not more than that (ADD THIS TO FCs!).
There is one Math question I couldn't solve even on my second try, and when I checked the answer, I still didn't get it! I don't understand the solution, and am probably understanding the question wrong. I'll add it here later. I've asked a friend to look into it and let me know.

VERBAL

Category	R	W	U	% Correct
Sentence Corr.	13	2	0	87%
Red Pencil Fever	1	0	0	100%
Idiom	3	1	0	75%
Verb Tense	2	0	0	100%
Subject/Verb Agreement	1	0	0	100%
Pronouns	1	0	0	100%
Parallel Construction	4	0	0	100%
Quantity Words	1	0	0	100%
Misc	0	1	0	0%
Arguments	11	1	0	92%
Weaken	3	1	0	75%
Assumption	5	0	0	100%
Resolve/Explain	1	0	0	100%
Strengthen	2	0	0	100%
Reading Comp.	9	5	0	64%
RC General	2	1	0	67%
RC Specific	5	4	0	56%
RC Reasoning	2	0	0	100%

I started reviewing the Verbal part here in office, but got stuck with the solution of the first wrong answer itself! It's an SC question, and my God! What solutions! I may be good at Verbal and may assume I write grammatically correct sentences, but I am completely unaware of technical explanations for why one answer is better than another! I've always been dependent on what sounds right to my ear, because I thought my extensive reading would be of help. Apparently, not on the GMAT! Hmmm...thinking of picking up MGMAT SC book. Anyway, I'll add to this when I get back home.