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What is the value of n?

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What is the value of n?  [#permalink]

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New post 30 Jan 2015, 07:17
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A
B
C
D
E

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65% (02:10) correct 35% (01:55) wrong based on 107 sessions

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Re: What is the value of n?  [#permalink]

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New post 30 Jan 2015, 07:33
1
1
A.
36n - n^2 >= 324
n(36-n)>=324..
Now 18*18 =324....If we keep n = 18...36-n = 18...satisfying !!!!!!
If we increase to 19...then 19*17 = 323...going on 20*16 = 320.....Not satisfying.
Also n can't be negative too....Because eqn will always be -ve*+ve so never satisfying.
Only conclusion n =18.
Sufficient

B.
325 > n^2 > 323
Now n can be -18 or +18 not sure...

So only confirmation = A....
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Re: What is the value of n?  [#permalink]

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New post 30 Jan 2015, 11:07
1
My answer is E.
Solving equation 1, we get (n-18)(n-18) is <=0
therefore, n is less than or equal to 18. no solid value for n.

2) same reason, n can be any number (non integers too) which satisfy both sides of the inequality.

Even putting them together gives us nothing, therefore E
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Re: What is the value of n?  [#permalink]

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New post 30 Jan 2015, 11:58
usre123 wrote:
My answer is E.
Solving equation 1, we get (n-18)(n-18) is <=0
therefore, n is less than or equal to 18. no solid value for n.

2) same reason, n can be any number (non integers too) which satisfy both sides of the inequality.

Even putting them together gives us nothing, therefore E


I guess you are right....E is the correct answer....Messed up the first eqn
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Re: What is the value of n?  [#permalink]

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New post 30 Jan 2015, 12:55
Hi All,

There is one important detail worth noting about this DS prompt: The prompt does NOT state that N is an integer.

Hi usre123,

Your deduction that N is less than or equal to 18 is incomplete (for example, N CANNOT be 10). There is a "lower boundary" for what N can equal.

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Re: What is the value of n?  [#permalink]

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New post 30 Jan 2015, 13:38
1
Can anyone look at my solution and point out my mistakes. Thank you!

(1) Sufficient. 36n ≥ n^2 + 324
36n -n^2 - 324 ≥ 0 /*(-1)
n^2 -36n + 324 <=0
(n-18)*(n-18)<=0
n<=18, however checking values we find that only n=18 satisfies the inequality, because anything that is < or > than 18 makes the inequality invalid. Even the value of 17.99 does not satisfy the inequality.

(2) Insufficient. 325 > n^2 > 323, by number testing we find that n can be between 18.01 and 17.99

Answer A
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Re: What is the value of n?  [#permalink]

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New post 31 Jan 2015, 01:25
Looks to me like the A's have it. Note that we end up with a perfect square that is <=0. A perfect square can't be less than 0, so it has to *be* 0, making x=18.
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Re: What is the value of n?  [#permalink]

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New post 31 Jan 2015, 06:01
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Satyarath wrote:
usre123 wrote:
My answer is E.
Solving equation 1, we get (n-18)(n-18) is <=0
therefore, n is less than or equal to 18. no solid value for n.

2) same reason, n can be any number (non integers too) which satisfy both sides of the inequality.

Even putting them together gives us nothing, therefore E


I guess you are right....E is the correct answer....Messed up the first eqn



hi stayarth and user123..
statement one is sufficient because simplifying we get (x-18)^2=<0.. only 0 satisfies the value and any other value will result in some +ive number/fraction <0 which will be wrong...
statement two is wrong not only because it can be 18 or -18 but it can also be a fraction, say 18.001 etc
so ans A
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Re: What is the value of n?  [#permalink]

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New post 31 Jan 2015, 06:22
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Bunuel wrote:
What is the value of n?

(1) 36n ≥ n^2 + 324
(2) 325 > n^2 > 323


Kudos for a correct solution.

The OA will be revealed on Sunday


Answer A

Statement 1:
36n>=n^2+324
n^2-36n+324<=0
(n-18)^2<=0
A square number cannot be < 0
So, (n-18)^2=0
and n-18 = 0
n=18
Sufficient

Statement 2:
n^2 can be any number (not just integer) between 323 and 325. So there are multiple values for n^2 and hence for n. Even if n^2=324, n = +18 or -18.
Insufficient

Answer: A
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Re: What is the value of n?  [#permalink]

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New post 31 Jan 2015, 19:25
1
Bunuel wrote:
What is the value of n?

(1) 36n ≥ n^2 + 324
(2) 325 > n^2 > 323


Kudos for a correct solution.

The OA will be revealed on Sunday


Statement 1: n^2 - 36n + 324 ≤ 0
324: (2^2)*(3^4)
(n-18)(n-18) ≤ 0
n=18
Sufficient

Statement 2: 325 > n^2 > 323
n^2 could be 324 so n could be +18 or -18 or even a a non-integer
Insufficient

Answer: A
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Re: What is the value of n?  [#permalink]

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New post 31 Jan 2015, 19:57
1
Bunuel wrote:
What is the value of n?

(1) 36n ≥ n^2 + 324
(2) 325 > n^2 > 323


Kudos for a correct solution.

The OA will be revealed on Sunday



(1) Rearranging,

n^2 - 36 n +324 <=0

quadratic equation, solve for n, when n=18, equation = 0... when n < 18, equation > 0 (i.e not within the boundary), When n >18 also equation > 0. Therefore n=18 (sufficient)

(2) n^2 is between 323 and 325. (This is a short cut and should be used carefully) since we already know that n=18, we can assume that this statement means n^2 = 324. However, we know roots of a perfect square can be either positive or negative, i.e n = +/- 18. (Insufficient)

Correct answer is A
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Re: What is the value of n?  [#permalink]

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New post 31 Jan 2015, 21:31
thank you everyone, I see my error now!
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New post 02 Feb 2015, 04:17
Bunuel wrote:
What is the value of n?

(1) 36n ≥ n^2 + 324
(2) 325 > n^2 > 323


Kudos for a correct solution.

The OA will be revealed on Sunday


VERITAS PREP OFFICIAL SOLUTION:

A. You should immediately recognize the familiar symptoms of a quadratic equation in statement 1, even if it's a "quadratic inequality or equation." If you arrange that statement to look like a quadratic so that you can factor, you'll find:

0≥n^2−36n+324
Which factors to:

0≥(n−18)^2
And here's where you need to think strategically and logically - the only way for 0 to be "greater than or equal to" anything squared is for that squared term to be 0, as nothing squared can be negative. So this statement, while it may not immediately look like it, guarantees that (n−18)=0, so n=18. Statement 1 is sufficient.

Statement 2 is not sufficient, as it allows for multiple noninteger values of n, so the answer is A.

One big lesson from this problem - Data Sufficiency questions are written very precisely; had "greater than or equal to" been "less than or equal to" statement 1 would not have been close to sufficient. Precision-in-language (and symbology) matters!!
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