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Which of the following series of numbers, if added to the

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Kudos [?]: 53 [0], given: 20

Which of the following series of numbers, if added to the [#permalink] New post 26 Jan 2012, 11:35
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  35% (medium)

Question Stats:

58% (02:38) correct 42% (01:19) wrong based on 59 sessions
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
[Reveal] Spoiler: OA
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Joined: 02 Sep 2009
Posts: 18730
Followers: 3240

Kudos [?]: 22371 [0], given: 2616

Re: set’s mean [#permalink] New post 26 Jan 2012, 11:46
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This post was
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rohitgoel15 wrote:
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


Mean of the given set is (1+6+11+16+21)/5=11.

Now, in order the mean not to change, the mean of the new set we add to the old one should also be equal to 11 (or as in all 3 new sets there are 3 numbers, then their sum must be 3*11=33). Let's check:

I. 1.5, 7.11 and 16.89 --> will end with 0.5 son not 33. Discard.
II. 5.36, 10.7 and 13.24 --> will end with 0.3 son not 33. Discard.
III. -21.52, 23.3, 31.22 --> -21.52+23.3+31.22=-21.52+54.52=33. Correct.

Answer: C (III only).
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Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 18730
Followers: 3240

Kudos [?]: 22371 [0], given: 2616

Re: Which of the following series of numbers, if added to the [#permalink] New post 23 May 2013, 04:38
Expert's post
Re: Which of the following series of numbers, if added to the   [#permalink] 23 May 2013, 04:38
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