sequence S = { 2, 4, 6, ..., 24 } You make sequence M by

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sequence S = { 2, 4, 6, ..., 24 } You make sequence M by [#permalink]

24 Nov 2005, 07:29

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sequence S = { 2, 4, 6, ..., 24 }

You make sequence M by removing 2 elements from sequence S.

What is the standard deviation of sequence M ?

(1) The average of sequence M and the average of sequence S are same.
(2) Sequence M does not contain 22.

(Please explain in detail...thank you)
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24 Nov 2005, 07:52

1. We could remove any two numbers that add up to 26 and get a different standard deviation. Insuff.

2. Remove 22 and then remove either 2, 4, or 6 and the standard deviation changes. Insuff

Together 22 and 4 must be removed. We can calculate the SD. suff.

(C)

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Re: DS - Sequence [#permalink]

24 Nov 2005, 09:51

C. if 22 s removed from the sequence, 4 must also be removed to make the same mean.

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24 Nov 2005, 14:13

C)...to calc the stdv of m we need to know the exact sequence of m. av of evenly spaced numbers is (first number+last number)/2. av of s is 13 and sum is 156. av of m is 13 and sum is 130. diff is 26.

1) we know the av, the sum and the diff of m and s. not enough. insuff
2) 22 is removed. not enough. insuff
1)+2) diff is 26. 22 is remove. 4 is left. we know the exact sequence of m and can calc the stdv.
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24 Nov 2005, 17:33

Good job, everyone.

As always, you guys are brilliant.

The OA is, as everybody already said, (C).
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[#permalink] 24 Nov 2005, 17:33

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sequence S = { 2, 4, 6, ..., 24 } You make sequence M by

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sequence S = { 2, 4, 6, ..., 24 } You make sequence M by

sequence S = { 2, 4, 6, ..., 24 } You make sequence M by

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