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# Veritas Prep PS Forum Expert - Karishma - Ask Me Anything about Math

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Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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19 Mar 2019, 19:04
1
Sandeepanisha wrote:
Hi karishma,
I need help in this question
1/ (statistics) 21 students took an exam. What is the number of students whose scores are at least the average (arithmetic mean) score of them?
1) The average (arithmetic mean) score of them is 78

2) The median score of them is 78

Hey Sandeepanisha,

We have 21 total students. We need those who scored >= Average

1) The average (arithmetic mean) score of them is 78
Not sufficient. We don't know how many scored at or above average and how many scored below average. There are many cases possible.
E.g. All 21 students scored exactly 78.
or 1 student scored 77, 19 students scored 78 and 1 student scored 79
and so on...
Number of students who scored >= average will be different in each case.

2) The median score of them is 78
Median score is the 11th score (middle) when all are arranged in increasing order. Again, multiple cases are possible.
E.g. All 21 students scored exactly 78. (so 11th score is also 78)
or 1 student scored 77, 19 students scored 78 and 1 student scored 79 etc (so 11th score is also 78)
and so on...
Number of students who scored >= average will be different in each case.

Using both statements, even if we know that the average is 78 and median is 78 too, still multiple cases are possible. Both examples discussed above hold and number of students who scored atleast average is different in both examples.

_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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22 Mar 2019, 04:19
1
Sandeepanisha wrote:
Thanks karishma ,really appreciated your Help.
I need to ask one more Question

In the xy-plane, a circle with the center of the origin has the x- intercepts of P(50,0) and R(-50,0). If Q is a point on the circle, what is the length of PQ?

1) The x-coordinate of Q is -40

2) The y-coordinate of Q is -30

Since the circle has the centre at origin, the distance between the two x intercepts will give the diameter. So the diameter is 100. This means the radius of the circle is 50.
Attachment:

Screenshot 2019-03-22 at 16.34.18.png [ 19.27 KiB | Viewed 457 times ]

For the length of PQ, we need the coordinates of P and Q. We already know that P(50, 0). Now we just need the coordinates of Q.

1) The x-coordinate of Q is -40

Note in the diagram above that there will be 2 points (Q' and Q'') on the circle which will have x coordinate of -40. But distance of each from P will be the same since Q' and Q'' are a reflection of each other across the x axis. So in both cases, PQ will be defined and will take the same value.
Hence this statement is sufficient alone.

2) The y-coordinate of Q is -30

Again, there will be 2 points (Q'' and Q''') where y coordinate will be -30.
Q'' will be much farther from P than Q''' so depending on the x co-ordinate of Q, the length of PQ will vary. Hence this statement is not sufficient alone.

_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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24 Mar 2019, 20:22
1
Sandeepanisha wrote:
Thanks Karishma,
I have a quick question:

The 3 ships will transport goods. Of all of the goods, 1/3 is transported by the first ship. And, of the remained goods, 1/3 is transported by the second ship and also, of the remained goods after 2 times transports, 1/3 is transported by the third ship. If the remained goods are 40 tons finally, what is the total weight of the goods before transports, in tons, originally?

Hey Sandeepanisha,

What is the source of this question? I don't know where the problem lies - Either the language of the original question is very unclear or you need to put down the question verbatim.

First ship => 1/3 goods
Remaining => 2/3 goods

Second ship => (1/3) of Remaining = (1/3)*(2/3) = 2/9
Remaining now => 2/3 - 2/9 = 4/9

Third ship => (1/3) of (4/9) = 4/27
Remaining now => 4/9 - 4/27 = 8/27

This Remaining now (8/27 of total originally) is given to be 40 tonnes
Total originally = 40*(27/8) = 135 tonnes
_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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24 Mar 2019, 20:28
1
Sandeepanisha wrote:
Hi Karishma,
In a certain flower bed, the flower X species with only green color and yellow color accounts for 3/8 of all flowers. If the flowers with green color account for 3/4 of the flower X species, what fraction of all flowers in the flower bed are yellow colors?

A. 1/32 B. 1/16 C. 3/32 D. 1/8 E. 5/32

Same comment for this question too.

Say there are total 32 flowers.

Flower X = (3/8)*32 = 12

Green colour accounts for (3/4)th of 12 so yellow account for (1/4)*12 = 3 flowers.

Fraction of yellow flowers = 3/32
_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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23 May 2019, 23:33
1
indu1954 wrote:
Car A drives from M to N at a constant rate of 50 miles per hour and after 1-hour starting car A, car B drives from N to M at a constant rate of 60 miles per hour. If the distance between M and N is 490 miles, then when they meet, what is the distance that moved by car A, in miles?
A. 200miles B. 220miles C. 240miles D. 250miles E. 260miles

In 1 hr, car A travels 50 miles. Now distance between car A and car B is 490 - 50 = 440 miles

This distance is covered by both together car A at 50 mph and car B at 60 mph

When they meet, time taken = 440/(50 + 60) = 4 hrs
In 4 hrs, car A would have traveled = 50 *4 = 200 miles

In all, car A traveled 200 + 50 = 250 miles
_________________
Karishma
Veritas Prep GMAT Instructor

BSchool Moderator
Joined: 08 Dec 2013
Posts: 794
Location: India
Concentration: Nonprofit, Sustainability
Schools: ISB
GMAT 1: 630 Q47 V30
WE: Operations (Non-Profit and Government)

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24 May 2019, 16:57
1
sandeepansiha121 wrote:
Hi,
Need Help to Solve this problem,
/(set) Of 250 students in a certain class, 80 students learn English and 96 students learn French. When the number of students who learn neither English nor French is 3 times the number of students who learn both English and French,
what is the number of students who learn both English and French?

A. 37 B. 36 C. 39 D. 42 E. 45

Hello sandeepansiha121 please check the diagram

Attachment:

IMG_20190525_062333.jpg [ 1.97 MiB | Viewed 550 times ]

Now let's form the equation-> Total students= Students-French + Students-Only English + (Students neither French, nor English)
250 = 96 + (80-x) + 3x
x= 37 (A)
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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25 May 2019, 01:45
1
indu1954 wrote:
*(probability) 4 traffic lights A, B, C, D have red light. If the probabilities that the red lights of A, B, C, and D hold are 0.5, 0.6, 0.7, and 0.8, respectively, what is the probability that a car passes by A and D and stops B and C, approximately?
A. 4% B. 7% C. 10% D. 15% E. 40%

_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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25 May 2019, 01:49
1
sandeepansiha121 wrote:
Hi,
Need Help to Solve this problem,
/(set) Of 250 students in a certain class, 80 students learn English and 96 students learn French. When the number of students who learn neither English nor French is 3 times the number of students who learn both English and French,
what is the number of students who learn both English and French?

A. 37 B. 36 C. 39 D. 42 E. 45

Hey sandeepansiha121,

Total = n(A) + n(B) - Both + Neither

Assuming, number of people who learn Both = x, number of people who learn Neither = 3x

250 = 80 + 96 - x + 3x
x = 37

_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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16 Jun 2019, 22:00
1
GittinGud wrote:
Hi VeritasKarishma, Can you please tell me most important quant topics I need to cover. I have a booked GMAT next week. I thought I was good at quant so I concentrated mostly on my verbal ability. Now my mock score is only 45. My target is 50/51. I am ready to put in 100 hours this week.Thanks!

Number Properties, Algebra and Geometry are the most important topics. Also, ensure that you understand the Data Sufficiency format really well. What is sufficiency, how to avoid common traps etc.
_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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01 Aug 2019, 20:15
1
Nums99 wrote:

I had a doubt and its not clear to me yet.

If xyz ≠ 0, xy > 0, and x^2 + xy + xz < 0, then which of the following must be true?

I. x(y + z) < 0

II. x + y + z < 0

III. If x < 0, then z > 0.

A) I only
B) I and II only
C) I and III only
D) II and III only
E) I, II, and III

xyz ≠ 0 implies none of x, y and z is 0.

xy > 0 implies both x and y have the same sign. Either both are positive or both negative.

x^2 + xy + xz < 0 implies xz is negative so x and z have opposite signs. x^2 is positive because squares cannot be negative. xy is positive we have already benn given so xz must be negative.

I. x(y + z) < 0

We know that the expression x^2 + xy + xz is negative
x^2 must be positive. So if we remove x^2 from above, the expression (xy + xz) will become even more negative.
Hence, this must be true.

II. x + y + z < 0
x^2 + xy + xz < 0
x(x + y + z) < 0
If x is positive, (x+y+z) < 0
If x is negative, (x + y + z) > 0 (Take x = -3, y = -1 and z = 100 for example)
So this is not necessarily true.

III. If x < 0, then z > 0.
Correct. x and z have opposite signs. So this must be true.

_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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19 Sep 2019, 04:59
1
Xin Cho wrote:
When I have a PS problem such as $$3^{-2x} + 3^{-x}$$ - 12 = 0 how should I approach this problem?

Second, related to the above, I have realized that I am oftentimes confused by $$2^{2+x}$$ = $$2^2*2^x$$ and $$2^{2x}$$ = ($$2^{x}$$)*($$2^{x}$$). Usually, what I do is I make up numbers and variables to see how it works. However, this takes considerable time and is not exactly the best technique under pressure. Thus, I am wondering if you can recommend some drill or daily exercise that would help me to solidify these differences.

Put 3^{-x} = a and then take it from there.

a^2 + a - 12 = 0
(a + 4)(a - 3) = 0
a = -4 or 3

3^{-x} cannot be negative because the base 3 is positive. So no matter what the exponent, it will not make a negative number.

3^{-x} = 3 = 3^1
-x = 1
x = -1

Also check the following posts on our blog:
https://www.veritasprep.com/blog/2011/0 ... eparation/
https://www.veritasprep.com/blog/2011/0 ... ration-ii/
https://www.veritasprep.com/blog/2011/0 ... s-applied/
_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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19 Sep 2019, 05:03
1
Xin Cho wrote:
When I have a PS problem such as $$3^{-2x} + 3^{-x}$$ - 12 = 0 how should I approach this problem?

Second, related to the above, I have realized that I am oftentimes confused by $$2^{2+x}$$ = $$2^2*2^x$$ and $$2^{2x}$$ = ($$2^{x}$$)*($$2^{x}$$). Usually, what I do is I make up numbers and variables to see how it works. However, this takes considerable time and is not exactly the best technique under pressure. Thus, I am wondering if you can recommend some drill or daily exercise that would help me to solidify these differences.

Practice questions on exponents (we have some drills in our skill builder if you have access to Veritas curriculum). Also, you can search the forum by selecting exponents tag and practice those questions. With a bit of practice, you will not get confused. Checking with numbers is a huge waste of time.
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Karishma
Veritas Prep GMAT Instructor

Manager
Joined: 29 Oct 2015
Posts: 243

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19 Sep 2019, 15:08
1
A bus stop is served by express buses, which run every hour at ten minutes past the hour, and local buses, which run every quarter of an hour, starting at five past the hour. What is the probability that a passenger arriving at the stop at random will have to wait more than six minutes for a bus?

A) 1/2
B) 31/60
C) 29/60
D) 1/15
E) 11/20
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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14 Nov 2019, 19:23
1
Lionila wrote:
Dear Karishma,

Unfortunately, I don't have the answer choices BUT I think I understood where the fault in my logic was. For some reason I thought that a+b can only be negative or positive. But because it is an inequality, there is a range of possibilities for x. I am quite confident now that the solution for that range is 1 =<x<5.

Am I off in my thinking?

Best,
Lionila

Yes Lionila, the correct range is 1 <= x < 5.
_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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08 Jun 2020, 22:52
1
1
nikitamaheshwari wrote:
Hi karishma

If you have articles on Speed/Distance/ Time, Work/ Rate, Geometry/ Coordinate Geometry and Probability, please let me know.
Also, if you have collated lists of all your articles - please do share. - Bunuel - If you can help with the same.

Thanks a lot.

Hey nikitamaheshwari:

Check these out:

https://www.veritasprep.com/blog/catego ... =work+rate
https://www.veritasprep.com/blog/catego ... m/?s=speed
https://www.veritasprep.com/blog/catego ... s=geometry
https://www.veritasprep.com/blog/catego ... robability

The first few posts on each link give you relevant discussions.
_________________
Karishma
Veritas Prep GMAT Instructor

Intern
Joined: 22 Jul 2018
Posts: 28

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10 Jun 2020, 08:45
1
Montyyy95 wrote:
HI karishma, i had a doubt in on question from Veritas prep book;

30% of consumers like only product A, and for every consumer that likes only product B, 3 also like product A. If 18% of consumers like neither product, what
percentage likes both?

Solution
Again draw out the diagrams, paying special attention to the ratio wording (for every consumer that likes B only, 3 like both). Since 48 of the 100 consumers
are accounted for by only A and NEITHER, then 3x + x must equal 52. 4x = 52 and x = 13, so 3x = 39. Both = 39% consumers.

I didnt get the solution; how it inferred the bolded portion?

Hey Montyyy95:

"for every consumer that likes only product B, 3 also like product A"

means for every 1 consumer that liked ONLY B, there are 3 consumers that liked A 'ALSO' which means that these 3 liked B as well as A.
This means ratio of
(ONLY B) : (B and A) = 1 : 3

Hope this clarifies! Let me know.

Thanks a lot karishma (glad to know how the word also made the difference!!)
Manager
Joined: 25 Aug 2016
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WE: Information Technology (Computer Software)

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07 Oct 2018, 21:03
Hello Karishma,

I am realty struggling with getting off with quant,can you help me decide a startergy what should I practice to start off,what resources to use and build up my quant skills. Thanks

Posted from my mobile device
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10685
Location: Pune, India

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08 Oct 2018, 02:11
Shrinidhi wrote:
Hello Karishma,

I am realty struggling with getting off with quant,can you help me decide a startergy what should I practice to start off,what resources to use and build up my quant skills. Thanks

Posted from my mobile device

Shrinidhi,

Please provide me details on your current level of prep in as much detail as possible. Here is an idea of things you need to cover:

Have you taken a prep test? If yes, what was your score? Your Q/V split? Your accuracy in easy/medium/hard questions?
Have you run through the complete curriculum of a test prep company? OG?
How comfortable are you with basic Arithmetic, Algebra etc?
_________________
Karishma
Veritas Prep GMAT Instructor

Intern
Joined: 07 Jul 2018
Posts: 9
Location: India
GMAT 1: 670 Q49 V32
GPA: 3.2
WE: Medicine and Health (Consulting)

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08 Oct 2018, 02:54
Thank you Karishma for taking your time out and helping us.

I recently gave my GMAT and got a very low GMAT score. I was more disappointed with my Q 47. On the test day, I took more than 2 mins on tougher questions especially DS. I had problems solving DS since the start of my prep. GMAT club quant tests helped me a lot, but I always fear on DS that I might be missing something else. "Should I plug more ? Did I plug in enough ?" And that attitude ultimately killed my test.

Even though I practiced many questions on this club on Functions and Inequalities, as I am uncomfortable with those topics, on test day, GMAT threw surprises and I succumbed.

Shed some light on to how to stop being overcautious on DS and few tips on handling Functions and Inequalities questions.

Posted from my mobile device
Current Student
Joined: 04 Jun 2018
Posts: 158
GMAT 1: 610 Q48 V25
GMAT 2: 690 Q50 V32
GMAT 3: 710 Q50 V36

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08 Oct 2018, 03:22
HI Karishma

It really is helpful to read all of your posts. I have made it a habit to go through your posts everyday, and it really helps me a lot.

So The problem I am facing right now is time management. I have my Gmat on the 4th of November.
My lowest score on the Quant gmat club tests was 44 and the highest was 49. I mostly stay around 47-48-49.

According to my targets, I have to score Q50.
The only topics on which I have not solved 700 level questions are Probability, P and C, Statistics and coordinate geometry. I am slightly under confident in Geometry.
So out of these topics, what should I ideally cover?
I would like to believe that my basics on these topics are not bad.

Also it would be great if you could help me from where I could cover any of these topics efficiently.

Regards
Re: Veritas Prep PS Forum Expert - Karishma - Ask Me Anything about Math   [#permalink] 08 Oct 2018, 03:22

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