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Is y a multiple of 15?

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Is y a multiple of 15? [#permalink]

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Is y a multiple of 15?

(1) y^2 is a multiple of 15
(2) The square root of y is a multiple of 15

[Reveal] Spoiler:
Every now and then I miss one scenario and end up getting the question wrong.
Need to know if there are any set of specific checks that I can perform on these kind of questions so that I do not miss any scenario.

Please help.
I will provide OA after some discussion.
[Reveal] Spoiler: OA

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Last edited by Bunuel on 18 May 2015, 03:35, edited 1 time in total.
Edited the question and added the OA.
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Re: Is y a multiple of 15? [#permalink]

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New post 17 May 2015, 10:09
ques asks
is y =0,15,30,etc

statement 1: y*y=0,15,...15*15...
no when 15
yes when 15*15

statement 2: sqrt y=0,15...
yes always

B is sufficient
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Re: Is y a multiple of 15? [#permalink]

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Hi 282552,

DS questions often include a 'test of your thoroughness' - in real simple terms, "do you see more than just the obvious possibilities?"

Here, we're asked if Y is a multiple of 15. This is a YES/NO question. Before you begin working on the two Facts, ask yourself this:

"Do we know ANYTHING about the value of Y?"

Starting off, the answer is NO - there are NO restrictions on the value of Y.... So Y could be positive, negative, zero, a fraction, a square root, some crazy repeating decimal, etc. Most Test Takers only think about the 'obvious' possibilities (positive integers), but you MUST consider the alternatives if you want to make sure that you're choosing the correct answer.

In Fact 1, we're told that Y^2 is a multiple of 15, but that does NOT mean that Y is a multiple of 15. Be thorough with your thinking, look for alternatives, ask yourself if there's anything else that's possible....and you'd be surprised how easy it can be to find those other possibilities.

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Re: Is y a multiple of 15? [#permalink]

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New post 18 May 2015, 03:37
282552 wrote:
Is y a multiple of 15?

(1) y^2 is a multiple of 15
(2) The square root of y is a multiple of 15

Every now and then I miss one scenario and end up getting the question wrong.
Need to know if there are any set of specific checks that I can perform on these kind of questions so that I do not miss any scenario.

Please help.
I will provide OA after some discussion.


You must provide the OA from the beginning.
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Re: Is y a multiple of 15? [#permalink]

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New post 18 May 2015, 04:55
Test It

Statement 1 - Y = 15 ....yes
Y is equal to Sqrt15------No insufficient

Statement 2 Sqrt of Y is a multiple of 15, that means that the prime factors of Y contain the prime factors of 15
Sufficient
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Re: Is y a multiple of 15? [#permalink]

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New post 27 May 2015, 12:43
1. y^2 is a multiple of 15

let y^2= 30= 15*2

y= \sqrt{15*2} which is definitely not a multiple of 15

let y^2= 225= 15*15

then y= \sqrt{225} = 15 (multiple of 15)

hence this statement is not sufficient

2. \sqrt{y} is a multiple of 15

let \sqrt{y}= 30

then y= 30^2= 15^2 * 2^2

this is definitely a multiple of 15

Hence second statement is sufficient.

Answer B
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Re: Is y a multiple of 15? [#permalink]

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282552 wrote:
Is y a multiple of 15?

(1) y^2 is a multiple of 15
(2) The square root of y is a multiple of 15


since we are not explicitly told that y must be an integer, 1 is insufficient, because y might be sqrt(15), which is not a multiple of 15.

statement 2 alone says that sqrt(y)=multiple of 15. so y must be a multiple of 15 as well.
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Re: Is y a multiple of 15? [#permalink]

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New post 29 Jun 2016, 13:00
282552 wrote:
Is y a multiple of 15?

(1) y^2 is a multiple of 15
(2) The square root of y is a multiple of 15

[Reveal] Spoiler:
Every now and then I miss one scenario and end up getting the question wrong.
Need to know if there are any set of specific checks that I can perform on these kind of questions so that I do not miss any scenario.

Please help.
I will provide OA after some discussion.


(1) y^2 is a multiple of 15
what is y= 15 ^1/2. In this case y is not a multiple of 15 but y^2 is.

(2) The square root of y is a multiple of 15.
let's say square root of y = 15 (minimum value)
so y = 225 (minimum value)

All values >15 with y^1/2 being multiple of 15, y will be multiple of 15

B is the answer
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Re: Is y a multiple of 15? [#permalink]

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Re: Is y a multiple of 15?   [#permalink] 27 Aug 2017, 18:12
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