M=N+2

Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pm; Location: Milpitas, CA; Thanked: 1854 times; Followed by:523 members; GMAT Score:770

by Anurag@Gurome » Thu Sep 06, 2012 10:08 pm

grandh01 wrote:Given that m= n + 2, what is the value
of m^2+4m+4?

1) n=20
2) n^=400

OA IS D

m = n + 2
We want to find the value of mÂ² + 4m + 4.

(1) n = 20 implies m = 20 + 2 = 22
So, we can find the value of mÂ² + 4m + 4, as we know m; SUFFICIENT.

(2) nÂ² = 400 implies n = 20, -20
If m = 22, so we can find the value of mÂ² + 4m + 4, as we did in statement 1.
If m = -18, we get a different value of mÂ² + 4m + 4
No definite answer; NOT sufficient.

The correct answer is A.

Last edited by Anurag@Gurome on Thu Sep 06, 2012 10:21 pm, edited 1 time in total.

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neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 am; Location: Utrecht, The Netherlands; Thanked: 318 times; Followed by:52 members

by neelgandham » Thu Sep 06, 2012 10:12 pm

Thanks for the response Anurag, but can't n be -20 ?

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alex.gellatly: Master | Next Rank: 500 Posts; Posts: 435; Joined: Wed Nov 16, 2011 7:27 am; Thanked: 48 times; Followed by:16 members

by alex.gellatly » Thu Sep 06, 2012 10:19 pm

Anurag@Gurome wrote:
grandh01 wrote:Given that m= n + 2, what is the value
of m^2+4m+4?

1) n=20
2) n^=400

OA IS D
m = n + 2
We want to find the value of mÂ² + 4m + 4.

(1) n = 20 implies m = 20 + 2 = 22
So, we can find the value of mÂ² + 4m + 4, as we know m; SUFFICIENT.

(2) nÂ² = 400 implies n = 20
Again m = 22, so we can find the value of mÂ² + 4m + 4, as we did in statement 1; SUFFICIENT.

The correct answer is D.

Hold on now.... can't n=-20? Thus changing the value of our equation. I got A for this reason. I was surprised with the answer D. Am I missing something?

A useful website I found that has every quant OG video explanation:

https://www.beatthegmat.com/useful-websi ... tml#475231

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pm; Location: Milpitas, CA; Thanked: 1854 times; Followed by:523 members; GMAT Score:770

by Anurag@Gurome » Thu Sep 06, 2012 10:22 pm

Yes, n can be 20 and -20, both. I've edited my reply. The answer should be A here.

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