Mean 1

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ranjeet75: Master | Next Rank: 500 Posts; Posts: 242; Joined: Fri Aug 01, 2008 8:49 am; Location: Delhi; Thanked: 6 times

by ranjeet75 » Fri Feb 03, 2012 5:19 am

Which of the following series of numbers, if added to the set {1, 6, 11, 16, 21}, will not change the set's mean?

I. 1.5, 7.11 and 16.89 II. 5.36, 10.7 and 13.24 III. -21.52, 23.3, 31.22

(A) I only (B) II only (C) III only (D) I and III only (E) None

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Source: Beat The GMAT — Data Sufficiency | Fri Feb 03, 2012 5:19 am

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Fri Feb 03, 2012 6:08 am

Mean of 1,6,11,16,21 = 55/5 = 11

Now we are asked to find a set of numbers when added to this, the mean should not change
(or) in other words, the mean of the set added should also be = 11 (or) sum = 33.

Only III has sum = 33 - C

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