Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 21 Sep 2011
Posts: 2

Re: GMAT Math Book [#permalink]
Show Tags
19 Dec 2012, 01:17
thank you very much, very handy and useful



Intern
Status: pursuing a dream
Joined: 02 Jun 2011
Posts: 44
Schools: MIT Sloan (LGO)

Re: GMAT Math Book [#permalink]
Show Tags
15 Feb 2013, 23:15
Dear walker,
In page 89 there are some mistakes.
SLOPE AND QUADRANTS: 1. If the slope of a line is negative, the line WILL intersect quadrants II and IV. X and Y intersects of the line with negative slope have the same sign. Therefore if X and Y intersects are positive, the line intersects quadrant I; if negative, quadrant III. 2. If the slope of line is positive, line WILL intersect quadrants I and III. Y and X intersects of the line with positive slope have opposite signs. Therefore if X intersect is negative, line intersects the quadrant II too, if positive quadrant IV. 3. Every line (but the one crosses origin (0,0) OR parallel to X or Y axis OR X and Y axis themselves) crosses three quadrants. Only the line which crosses origin OR is parallel to either of axis crosses only two quadrants. 4. If a line is horizontal it has a slope of 0, is parallel to Xaxis and crosses quadrant I and II if the Y intersect is positive OR quadrants III and IV, if the Y intersect is negative. Equation of such line is y=b, where b is y intersect. 5. If a line is vertical, the slope is not defined, line is parallel to Yaxis and crosses quadrant I and IV, if the X intersect is positive and quadrant II and III, if the X intersect is negative. Equation of such line is x=a, where a is xintercept.
In addition, I would like to suggest some changes to the explanation of Lines in Coordinate Geometry (page 85). I think there are too many formulas and a systematic approach is not encouraged. For instance:
Page 85
I think using a b c on General Form is confusing. I would recommend to use A B C, such as:
\(Ax+By+C=0\)
The point intercept form is given right away, together with the slope and the yintercept for the General Form, all using the same letters. I would change the whole explanation to something like:
From the General Form \(Ax+By+C=0\),
\(By=AxC\)
\(\frac{B}{B}y=\frac{A}{B}x+\frac{C}{B}\)
\(y=\frac{A}{B}x+\frac{C}{B}\)
Where \(\frac{A}{B}\) is the slope and \(\frac{C}{B}\) is the yintercept. From here:
\(y=mx+b\).
This is a much more intuitive approach and does not require to remember 3 formulas.
Page 86
Why give the formula of a line passing through two points? Following an intuitive approach, I would just:
1. Calculate slope from the line crossing the two given points. 2. Plug in the slope and one of the points in the general equation to get b. No formulas required.
Page 87
Again, another formula is given. Same approach as above can be used with (x,0) and (0,y).
Page 92
Another formula is given. Why not just use the same slope and the point?
Maybe all the formulas can be included at the end as an extra, but using most of them right away somewhat breaks the logic and just give a takeaway that does not ensure that the concept is correctly understood. I think it's much more powerful (and simple!) to use logic and know where everything is coming from.
That come to mind, the basic and most important are: Distance, Mid Point, General Form, PointIntercept Form, Slope of a Line, Parallel lines = same slope, Perpendicular lines = negative reciprocal, Distance LinePoint.
Best Regards, and great job on this Math Book!



Intern
Joined: 06 Feb 2013
Posts: 42
Location: France
WE: Engineering (Other)

Re: GMAT Math Book [#permalink]
Show Tags
20 Feb 2013, 02:38
Hello to all,
My first post on this forum.
I have a question about the formulas to add an element to a set on p103. Are they also valid for sets which contain a limited amount of numbers, for example a set consisting of four or five numbers? If you use the number two formula, and you add a number to a small set, the mean will change significantly. I think this formula is only valid for large sets in which the mean is more or less invariable when adding numbers?
I just tried it with a small set of numbers, and the formula didn't work.



Intern
Status: pursuing a dream
Joined: 02 Jun 2011
Posts: 44
Schools: MIT Sloan (LGO)

Re: GMAT Math Book [#permalink]
Show Tags
20 Feb 2013, 10:11
jorisboris, I am not sure if I understand you, but so far I think you are misunderstanding the formulas (are you referring to the formulas labeled as 1), 2), 3) and 4) in p103?) Translated to words: 1) If the number you add to the set (y) is higher than the standard deviation (in formulas: if the distance from y to the median is higher than the distance of the standard deviation to the median, if y > STD) then the standard deviation of the set will increase (in formulas: the new standard deviation will be higher than the old standard deviation). Or what is the same: new numbers added to the set will reduce the STD if they present less deviation than the STD (they are closer to the mean than the STD range), will increase the STD if they are further away from the mean than the range of the STD, will keep the STD the same if they are exactly as far away from the mean as the STD and will minimize as much as possible the STD if they are exactly equal to the mean (they add a deviation of 0, so the STD has the same total deviation, +0 is added) but more term to divide, thus decreases as much possible). Of course if you have 5 terms and you add a 6th term to the set that is exactly the same as the mean the STD will decrease much more than if you have 1000 terms with a huge STD and you just add one new element to the set. Still, the behavior will be the same, as these considerations are QUALITATIVE, not QUANTITATIVE. Check my notes attached. In summary, these formulas only explain the behavior of the Standard Deviation based on the kind of number that you add to the set. Colors match, so line 1) refers to red point, line 2) refers to orange point, etc. Does this solve your question?
Attachments
STD.jpg [ 81.79 KiB  Viewed 4137 times ]



Intern
Joined: 06 Feb 2013
Posts: 42
Location: France
WE: Engineering (Other)

Re: GMAT Math Book [#permalink]
Show Tags
20 Feb 2013, 10:38
Hello LGOdream, thanks for your fast reply,
I was discussing the second formula in which a new element is added: sigma' = sigma if ymu = sigma.
I tried it with an example, a set containing four items: {1, 2, 3, 4}. The mean of this set is 2.5 and the standard deviation is (rounded) 1.118.
Add this standard deviation to the mean, giving: y = 2.5 + 1.118 = 2.618 and add this number to the set: {1, 2, 3, 4, 2.618}. The mean of this new set is 2.724, and the new standard deviation sigma' becomes 1.095.
The standard deviation sigma' of the new set is not equal to the standard deviation sigma of the first set, although ymu = sigma.
Is there something wrong in my reasoning here?
Greetings



Manager
Joined: 12 Dec 2012
Posts: 156
Location: Poland

Re: GMAT Math Book [#permalink]
Show Tags
13 Apr 2013, 05:54
Page 58, bottom: Where b is the length of the base, a and c the other sides; h is the length of the corresponding altitude; R is the Radius of circumscribed circle; r is the radius of inscribed circle; P is the perimeterThe Perimeter of the triangle (a+b+c) or of the in/circumscribed circle (2*pi*r /*R)?
_________________
If I answered your question with this post, use the motivating power of kudos!



Senior Manager
Joined: 23 Mar 2011
Posts: 462
Location: India
GPA: 2.5
WE: Operations (Hospitality and Tourism)

Re: GMAT Math Book [#permalink]
Show Tags
13 Apr 2013, 06:42
This is new for me....will sneak peak. But must say great effort walker...I am just starting quant
_________________
"When the going gets tough, the tough gets going!"
Bring ON SOME KUDOS MATES+++  Quant Notes consolidated: http://gmatclub.com/forum/consoloditedquantguidesofforummosthelpfulinpreps151067.html#p1217652 My GMAT journey begins: http://gmatclub.com/forum/mygmatjourneybegins122251.html All about Richard Ivey: http://gmatclub.com/forum/allaboutrichardivey148594.html#p1190518



Manager
Joined: 29 Aug 2013
Posts: 77
Location: United States
Concentration: Finance, International Business
GMAT 1: 590 Q41 V29 GMAT 2: 540 Q44 V20
GPA: 3.5
WE: Programming (Computer Software)

Re: GMAT Math Book [#permalink]
Show Tags
15 Sep 2013, 01:30
walker wrote: Hi, I couldn't find anything on Mixture/Weighted average problems. Can we have something from that area to in this book?



Math Expert
Joined: 02 Sep 2009
Posts: 39595

Re: GMAT Math Book [#permalink]
Show Tags
15 Sep 2013, 03:53



BSchool Forum Moderator
Joined: 27 Aug 2012
Posts: 1193

Re: GMAT Math Book [#permalink]
Show Tags
29 Sep 2013, 22:56
Hi bb/Bunuel/walker, Guys, for many chapters in the GC Math book, we don't have practice reference to OG 12(or any other edn.) problems unlike these chapters  Number Theory,Geometry, Coordinate Geometry... So,do we have any immediate plan to include the same (re practice reference to OG problems) in those chapters ( Standard deviation,Probability, Permutation & Combinations, Absolute value,Algebra,Remainders,Word problemsDST and Worktime relted, Overlapping Sets)? These additions will enrich the book overall,I think. Look forward to hear from you.
_________________
UPDATED : eGMAT SC ResourcesConsolidated  ALL RC ResourcesConsolidated  ALL SC ResourcesConsolidated  UPDATED : AWA compilations109 Analysis of Argument Essays  GMAC's IR Prep Tool
Calling all Columbia (CBS) MBA Applicants: (2018 Intake) Class of 2020 !!! NEW !!!
GMAT Club guide  OG 111213  Veritas Blog  Manhattan GMAT Blog
KUDOS please, if you like the post or if it helps



Intern
Joined: 08 Dec 2013
Posts: 21
Location: India
Concentration: General Management, Operations
GMAT 1: 710 Q50 V35 GMAT 2: 730 Q50 V38
GPA: 3.46
WE: Engineering (Manufacturing)

Re: GMAT Math Book [#permalink]
Show Tags
27 Dec 2013, 05:24
Hello people, I found an error on page 4 of the book. Actually its not an error but there's a shorter way to do the same thing. For verifying whether a no. (say n ) is prime or not we just need to check whether n is divisible by any prime no. less than sqrt(n).
We dont have to check if n is divisible by all the positive integers less than sqrt(n).
If n is not divisible by any prime no. less than sqrt(n), then n is a prime no.
(lets say if a no. is divisible by 6 then it will be divisible by 2 and 3.) To avoid any confusion : sqrt(n) means square root of n.



Manager
Joined: 23 May 2013
Posts: 126

Re: GMAT Math Book [#permalink]
Show Tags
27 Dec 2013, 20:55
hi all, Please can we have practice questions from QG13 included in Math book? It will be very helpful. Thanks
_________________
“Confidence comes not from always being right but from not fearing to be wrong.”



Math Expert
Joined: 02 Sep 2009
Posts: 39595

Re: GMAT Math Book [#permalink]
Show Tags
28 Dec 2013, 04:18



BSchool Forum Moderator
Joined: 27 Aug 2012
Posts: 1193

Re: GMAT Math Book [#permalink]
Show Tags
28 Dec 2013, 04:22
bagdbmba wrote: Hi bb/Bunuel/walker, Guys, for many chapters in the GC Math book, we don't have practice reference to OG 12(or any other edn.) problems unlike these chapters  Number Theory,Geometry, Coordinate Geometry... So,do we have any immediate plan to include the same (re practice reference to OG problems) in those chapters ( Standard deviation,Probability, Permutation & Combinations, Absolute value,Algebra,Remainders,Word problemsDST and Worktime relted, Overlapping Sets)? These additions will enrich the book overall,I think. Look forward to hear from you. Bunuel  Do we have any update on this? Thank you.
_________________
UPDATED : eGMAT SC ResourcesConsolidated  ALL RC ResourcesConsolidated  ALL SC ResourcesConsolidated  UPDATED : AWA compilations109 Analysis of Argument Essays  GMAC's IR Prep Tool
Calling all Columbia (CBS) MBA Applicants: (2018 Intake) Class of 2020 !!! NEW !!!
GMAT Club guide  OG 111213  Veritas Blog  Manhattan GMAT Blog
KUDOS please, if you like the post or if it helps



Current Student
Joined: 21 Oct 2013
Posts: 193
Location: Germany
GPA: 3.51

Re: GMAT Math Book [#permalink]
Show Tags
14 Feb 2014, 03:47
Bunuel wrote: ankur1901 wrote: hi all,
Please can we have practice questions from QG13 included in Math book? It will be very helpful. Thanks Done. Added the following link there:  Official Guide for GMAT® Review, 13th Edition Quantitative Question DirectoryHey Bunuel, the link doesn't work for me here can you give an update?



Math Expert
Joined: 02 Sep 2009
Posts: 39595

Re: GMAT Math Book [#permalink]
Show Tags
14 Feb 2014, 03:50



Current Student
Joined: 21 Oct 2013
Posts: 193
Location: Germany
GPA: 3.51

Re: GMAT Math Book [#permalink]
Show Tags
14 Feb 2014, 04:33
Thanks for the links. Since there are different practice questions for the different topics in the math book, and they vary from one edition to the other, can you give me a heads up on how you chose the questions for the different topics? This morning I finished number theory and started doing the questions when I realized that they were for edition 12, so I just looked at the question # and figured if they would be fitting for the topic. If not, I randomly chose a question which I THOUGHT would be OK to practice what I learned in the topic. But since I'm no expert on seeing whether it's one topic or another, maybe you could help me here? Would appreciate it!
Thanks!



Moderator
Joined: 20 Dec 2013
Posts: 189
Location: United States (NY)
GMAT 1: 640 Q44 V34 GMAT 2: 710 Q48 V40 GMAT 3: 720 Q49 V40
GPA: 3.16
WE: Consulting (Venture Capital)

Re: GMAT Math Book [#permalink]
Show Tags
04 Mar 2014, 00:42
Bunuel, Walker, Shrouded1, BB  hats off to you guys for writing this GMAT Quant book...you guys rock!
_________________
MY GMAT BLOG  ADVICE  OPINIONS  ANALYSIS



Intern
Joined: 09 Jun 2014
Posts: 5

Re: GMAT Math Book [#permalink]
Show Tags
09 Jun 2014, 02:49
Thanks for sharing with us great post.



Manager
Joined: 28 Dec 2013
Posts: 80

Re: GMAT Math Book [#permalink]
Show Tags
19 Jun 2014, 09:06
In the Math Book, page 26 , there is this problem : x^6  3x^3 + 2 = 0, then it states let y = x^3, then it goes to y^2  3y^3 + 2 (my first question is here, why is it 3y^3?, is it because y = x^3, so we are doubling?) next, this is factored to (y2) (y1) = 0 and the solutions are given as y = 1,2 (I understand this) or x^3 = 1,2 (I understand this) or x = 1, cube root 3 (this is where I am confused as to how there solns are found for x , and especially the cube root 3 i can't see where its coming from). Thank you in advance for the assistance.




Re: GMAT Math Book
[#permalink]
19 Jun 2014, 09:06



Go to page
Previous
1 2 3 4 5 6 7 8
Next
[ 157 posts ]




