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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: 9704
Location: Pune, India

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27 May 2019, 22:44
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%

Looking at the screenshot you sent, it looks like the question is exactly as you have written. I would suggest you to ignore this source since it seems to be very sub-standard.

As for this question, if the red light holds, the car stops. If it changes, the car passes through.

Probability that A and D turn while B and C hold = 0.5 * 0.6 * 0.7 * 0.2 = 4.2%
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Karishma
Veritas Prep GMAT Instructor

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Joined: 23 Apr 2016
Posts: 16
Location: India
Concentration: Entrepreneurship, General Management
GPA: 3.88
WE: Marketing (Consulting)

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06 Jun 2019, 14:24
Hi Karishma,
(geometry) Two people run the circle with 10 rounds, one runs in the inside and the other runs in the outside. When the difference between the inside and the outside is 15 feet, what is the difference of between two people's distance after running 10 rounds, approximately?
A. 800 B. 850 C. 900 D. 950 E. 1,000
Intern
Joined: 30 Jan 2019
Posts: 4
Location: India

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09 Jun 2019, 11:01
hi Karishma,
https://gmatclub.com/forum/as-the-pictu ... 31845.html
Intern
Joined: 02 Nov 2017
Posts: 27
Location: India
GPA: 3.87

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11 Jun 2019, 11:14
Need help to Solve the quant Question.

https://gmatclub.com/forum/geometry-297755.html
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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12 Jun 2019, 00:25
Sandeepanisha wrote:
Hi Karishma,
(geometry) Two people run the circle with 10 rounds, one runs in the inside and the other runs in the outside. When the difference between the inside and the outside is 15 feet, what is the difference of between two people's distance after running 10 rounds, approximately?
A. 800 B. 850 C. 900 D. 950 E. 1,000

I don't understand this question. It seems to say that one person runs 10 rounds outside and another person runs 10 rounds inside. If the difference in the circumference is 15 feet, the one outside will run 10*15 feet extra. If the difference of 15 feet is between radii or diameter, it will be different. The question needs to clarify properly.
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Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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12 Jun 2019, 00:26
ajaysharma121 wrote:
hi Karishma,
https://gmatclub.com/forum/as-the-pictu ... 31845.html

Hey ajaysharma121,

_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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12 Jun 2019, 00:27
indu1954 wrote:
Need help to Solve the quant Question.

https://gmatclub.com/forum/geometry-297755.html

Done.
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Karishma
Veritas Prep GMAT Instructor

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Joined: 02 Nov 2017
Posts: 27
Location: India
GPA: 3.87

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12 Jun 2019, 18:50
https://gmatclub.com/forum/geometry-297753.html
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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13 Jun 2019, 03:18
indu1954 wrote:
https://gmatclub.com/forum/geometry-297753.html

Hey indu1954,

The requested post doesn't exist anymore. Could you please check!
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Karishma
Veritas Prep GMAT Instructor

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Joined: 01 Jan 2019
Posts: 67
Concentration: Finance, Economics
GPA: 3.24

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13 Jun 2019, 03:26
Hi Karishma,

Weighted average is a gray area section for me, can you please help me in this problem.

https://gmatclub.com/forum/1-unit-of-x- ... 96986.html

Posted from my mobile device
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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13 Jun 2019, 03:55
Shef08 wrote:
Hi Karishma,

Weighted average is a gray area section for me, can you please help me in this problem.

https://gmatclub.com/forum/1-unit-of-x- ... 96986.html

Posted from my mobile device

Hey Shef08,

Done here: https://gmatclub.com/forum/1-unit-of-x- ... l#p2292835

If you struggle with weighted averages, check out this post: https://www.veritasprep.com/blog/2011/0 ... -averages/
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Karishma
Veritas Prep GMAT Instructor

Manager
Joined: 18 Feb 2018
Posts: 107

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16 Jun 2019, 00:13
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!
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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16 Jun 2019, 23:00
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.
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Karishma
Veritas Prep GMAT Instructor

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Joined: 12 Jan 2019
Posts: 32

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01 Aug 2019, 20:39

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

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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01 Aug 2019, 21:15
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.

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Karishma
Veritas Prep GMAT Instructor

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Joined: 12 Jan 2019
Posts: 32

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09 Aug 2019, 06:02

The product of 3 consecutive positive multiples of 4 must be divisible by each of the following EXCEPT:

A)16
B)36
C)48
D)128
E)192

The OA is B but i don't understand why exactly.
Arent all these numbers divisible by three consecutive multiples of 4
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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13 Aug 2019, 21:41
Nums99 wrote:

The product of 3 consecutive positive multiples of 4 must be divisible by each of the following EXCEPT:

A)16
B)36
C)48
D)128
E)192

The OA is B but i don't understand why exactly.
Arent all these numbers divisible by three consecutive multiples of 4

Say the 3 consecutive multiples are 4, 8 and 12. Their product = 4*8*12. This product is not divisible by 36.
36 = 4*9
The product does not have 9 in it (two 3s). It necessarily will have one 3 but it may or may not have two 3s. Hence it may not be divisible by 36.

Three consecutive multiples of 4 will have three 4s, another 2 and a 3 necessarily. So the product will be divisible by 2^7 * 3 and all its factors.

For more on this, check:
https://www.veritasprep.com/blog/2011/0 ... c-or-math/
https://www.veritasprep.com/blog/2011/0 ... h-part-ii/
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Karishma
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Joined: 12 Jan 2019
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25 Aug 2019, 04:38

https://gmatclub.com/forum/if-6-4-x-5-w ... 99799.html

i am really confused when they say " |x|=-x " isn't the only possibility to this that x = 0???

because no number inside a mod sign can be negative as such
Intern
Joined: 17 Aug 2018
Posts: 19

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25 Aug 2019, 19:34
tilak123 - I am kicking off this post as per your request.

This is a compilation of all links to the "Made Easy" series. Bunuel has already compiled links to all my posts on specific topics. I will provide links to those compilations:

Weighted Avgs and Mixtures Made Easy

Hi Karishma.. I request reference to Question 1 in your post "A group of 8 friends sit together in a circle. If A refuses to sit beside B unless C sits on the other side of A as well, how many possible seating arrangements are possible?" Even though i understood your explanation, can u please tell me whats wrong in my approach?

My Approach: There are 2 scenarios possible, One where A sits next to both B & C and the other wherein A doesn't sit next to both B & C . In the former the no.of arrangements are: 1*2*1*5*4*3*2*1= 2*5!
In the latter the no. of arrangements are: 1*5*4*5*4*3*2*1= 20*5!
Thus total no. of arrangements are: 5!(20+2)= 22*5!

Where am i missing??
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9704
Location: Pune, India

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25 Aug 2019, 21:12
Nums99 wrote:

https://gmatclub.com/forum/if-6-4-x-5-w ... 99799.html

i am really confused when they say " |x|=-x " isn't the only possibility to this that x = 0???

because no number inside a mod sign can be negative as such

Your assumption is that x is a positive number and hence, -x is a negative number. But can -x be a POSITIVE number? Think about it.

What about the case when x = -5? Then -x = - (-5) = 5

What about the case when x = -23? Then -x = - (-23) = 23

-x can be positive when x is negative. In these cases, -x = |x|

And hence, we define |x| as:

|x| = x when x >= 0
|x| = -x when x < 0
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Karishma
Veritas Prep GMAT Instructor

Re: Veritas Prep PS Forum Expert - Karishma - Ask Me Anything about Math   [#permalink] 25 Aug 2019, 21:12

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