Problem on mean..

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MI3: Senior | Next Rank: 100 Posts; Posts: 83; Joined: Sat Feb 26, 2011 11:22 amFollowed by: 1 member; Thanked: 1 times

by MI3 » Sat Jul 16, 2011 3:19 am

Q. The mean of (54,820)^2 and (54,822)^2 =
(A) (54,821)^2 (B) (54,821.5)^2 (C) (54,820.5)^2 (D) (54,821)^2 + 1 (E) (54,821)^2 - 1

IMO - C, am I correct?

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Source: Beat The GMAT — Problem Solving | Sat Jul 16, 2011 3:19 am

Frankenstein: Legendary Member; Posts: 1448; Joined: Tue May 17, 2011 9:55 amFollowed by: 53 members; Location: India; Thanked: 375 times

by Frankenstein » Sat Jul 16, 2011 3:27 am

Hi,
(a+b)^2 + (a-b)^2 = 2(a^2+b^2)
Use the same here
(54,820)^2 + (54,822)^2 = (54,821-1)^2 + (54,821+1)^2 =2[(54,821)^2 + 1^2]
So, average is 1/2[(54,820)^2 + (54,822)^2] = (54,821)^2 + 1

Hence, D

Cheers!

Things are not what they appear to be... nor are they otherwise

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ikaplan: Master | Next Rank: 500 Posts; Posts: 181; Joined: Fri Sep 04, 2009 12:06 pmFollowed by: 1 member; Thanked: 17 times

by ikaplan » Sat Jul 16, 2011 4:29 am

Thanks for the formula Frankenstein- I just updated my flash cards

"Commitment is more than just wishing for the right conditions. Commitment is working with what you have."

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