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Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
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GMAT 1: 760 Q51 V42 GPA: 3.82
Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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Again, GMAT Math is a test of logic. As long as you have a firm and strong grasp of logic of GMAT Math, you will be able to score high in the test.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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As stated in the post, you should remember that Integer and Statistics are the main chapters to focus for DS.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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We are not english experts as stated in the post. So please let us know if there are any mistakes to be corrected. Also, feel free to send us messages if you have any questions!
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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MathRevolution wrote:
This is also a 50-51 level question and is related to the common mistake type 4(A)
When 25 integers are there such that their average (arithmetic mean) is 100, is their median equal to 100?
1) They are consecutive
2) The average (arithmetic mean) of the greatest number and the smallest number of them is 100

There are 2 variables in the question. Hence, C could be the answer. However, since this is an integer question, we have to apply the common mistake type 4(A). Then, we can see that A is the correct answer.

Doesn't option 'B' says numbers are consecutive !

can someone advise pls
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Senior Manager  Status: Always try to face your worst fear because nothing GOOD comes easy. You must be UNCOMFORTABLE to get to your COMFORT ZONE
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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MathRevolution wrote:
This is a difficult inequality question.
(ex 6) *(inequality) If 0.01<a<0.02, 5,000<b<10,000, which of the following can be the value of (1/a2)+(1/b2)?
A. 0.2 B. 0.5 C. 750 D. 525 E. 7250

Can someone elaborate how to solve above problem
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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MathRevolution wrote:
There are some difficult PS questions that appear as 50-51 level questions.
In the x- y plane, there are 4 points (0,0), (0,4), (6,4), and (6,0). If these 4 points makes a rectangle, what is the probability that x+y<4?
A. 1/2 B. 1/3 C. 1/4 D. 1/5 E. 2/5
If we draw conditions on coordinates, the correct answer is B.

Please elaborate how to solve above question
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Math Revolution GMAT Instructor V
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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Please remember that GMAT Quant section is in CAT system. This means that you have to get as many easy questions as right in order to move on to 49-51 score level!
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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1
sairam595 wrote:
MathRevolution wrote:
There are some difficult PS questions that appear as 50-51 level questions.
In the x- y plane, there are 4 points (0,0), (0,4), (6,4), and (6,0). If these 4 points makes a rectangle, what is the probability that x+y<4?
A. 1/2 B. 1/3 C. 1/4 D. 1/5 E. 2/5
If we draw conditions on coordinates, the correct answer is B.

Please elaborate how to solve above question

Here is an answer to your question!
Attachments 1-st.jpg [ 2.24 MiB | Viewed 1076 times ]

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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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sairam595 wrote:
MathRevolution wrote:
This is a difficult inequality question.
(ex 6) *(inequality) If 0.01<a<0.02, 5,000<b<10,000, which of the following can be the value of (1/a2)+(1/b2)?
A. 0.2 B. 0.5 C. 750 D. 525 E. 7250

Can someone elaborate how to solve above problem

Here is an answer to your question!
Attachments 3-rd.jpg [ 2.37 MiB | Viewed 1071 times ]

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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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Questions related to Murphy's and Sally's law can appear as 51 level questions!
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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As always, questions combined with the mistake type 3 and 4 are given. Let's have a look at the example below. This is a very recent question, which also belongs to the mistake type 4(B). This question is on the level of score 50-51. You should be able to tackle a question like this. In addition, you should be aware of relation between approach method to variables and the mistake types.
Is 7-digit positive integer a,bcd,150 divisible by 6?
1) a,bcd,000 is divisible by 6.
2) a+b+c+d is divisible by 3.

Both C and D can be answers for this type of questions. This is a common mistake type 4(B) question which is in the level of 50-51.
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1
Please be careful on Common mistake type 4(B) questions.
When p, s, and t are positive integers, is p a factor of st?
1) p is a factor of s
2) t is a multiple of p

There are 2 variabes in the original condition. Hence, there is a high chance that C is the correct answer. Using con 1) & 2), C is the correct answer. However, since this is one of key questions, we can apply the common mistake type 4(B). Then, we get 1)=2). The answer is always yes and the condition is sufficient. Hence, the correct answer is D.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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If x, y are positive integers, what is the remainder when
(2^8x+6)+y is divided by 5?
1) x=3
2) y=1

This is a general common mistake type 4(A) question. There are 3 variables in the original condition. Hence, there is a high chance that E is the correct answer. Using 1) & 2), we get 2^30+1=~5. The remainder is 0. Hence, the correct answer is unique and the condition is sufficient – C is the correct answer. However, since it is one of key questions, we can apply the common mistake type 4(A). From (2^8x+6), we can see that the units digit is always 4. Hence, we only have to know 4. Thus, the correct answer is B.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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There are many difficult PS questions nowadays.
Which of the following is equal to (a^2)/|a|? (a is not zero)
I. |a| II. (|a|^2)/a III. |((a/|a|)^2)a|
A. I only
B. II only
C. III only
D. I & III only
E. II & III only

Since, (a^2)/|a|=(|a|^2)/|a|=|a|. The correct answer is D.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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This is a consecutive integers question.
If x, y, z are integers, is xyz a multiple of 3?
1) x+y+z is a multiple of 3
2) x, y, and z are consecutive

There is 1 variable in the original condition. Hence, there is a high chance that D is the correct answer. In case of con 1), we have (x,y,z)=(1,2,4) yes, (x,y,z)=(2,2,2) n. Hence, the condition is not sufficient.
In case of condition 2), if x, y, z are consecutive integers, they always have 3. Hence, the answer is yes and the condition is sufficient. Thus, the correct answer is B.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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When m and are positive integers, is 2m+2n divisible by 5?
1) m=n+2
2) n=3

There are 2 variables (a and b) in the original condition. There is a high chance that C is the correct answer. Using con 1) and 2), the correct answer is C. However, since this is one of key questions, if we apply common mistake type 4(A), using con 1), we get 2^m+2^n=(2^n+2)+2^n=(2^2+1)2^n=5(2^n). It is always divisibly by 5. The answer is yes and the condition is sufficient. Hence, the correct answer is A.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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Again, it is cruticial to get the first 20 questions right!!
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Please remember that DS questions will be a determinant for a perfect 51.
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Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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MathRevolution wrote:
This is a 50-51 level question

(ex 7) *(integer) What is the greatest common divisor of positive integers n and m?
1) n=1
2) m=n+1
There are 2 variables in the original condition (m, n). In order to match the number of variables and the number of equations, we need 2 equations. Hence, there is a high chance that C is the correct answer. Using 1) and 2), C is the correct answer. However, we have to utilize the common mistake type 4(B) since it is an integer question. The correct answer is D.

MathRevolution Could pls elaborate this que how the ans is D
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Math Revolution GMAT Instructor V
Joined: 16 Aug 2015
Posts: 8017
GMAT 1: 760 Q51 V42 GPA: 3.82
Re: The Ultimate Q51 Guide [Expert Level]  [#permalink]

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As stated in the post, in case of Absolute Value questions, a question regarding the relationship among |a|, a, and -a will determine a perfect 51.
_________________ Re: The Ultimate Q51 Guide [Expert Level]   [#permalink] 05 Sep 2016, 17:46

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