What is the value of n?

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

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.

GMAT assassins aren't born, they're made,
Rich

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

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.

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

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

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

(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

thank you everyone, I see my error now!

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!!

from 2) one can easily get to know that n = 18, now its n^2, which means it can be -18 or 18.

from 1) we can just use the value from B, n will be 18

because if you take any other value, the inequality will fail

A

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.