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A set of data consists of the following 5 numbers: 0,2,4,6 [#permalink]
24 Jan 2008, 15:08

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A set of data consists of the following 5 numbers: 0,2,4,6 and 8. Which 2 numbers, if added to create a set of 7 numbers, will result in a new standard deviation that is closest to the standard deviation for of the 5 original numbers?

A) -1 and 9 B) 4 and 4 C) 3 and 5 D) 2 and 6 E) 0 and 8

Sorry, I mistook and wrote d instead of 4 in B.

Last edited by netcaesar on 25 Jan 2008, 08:36, edited 1 time in total.

Re: PS: Standard Deviation [#permalink]
24 Jan 2008, 20:29

GMATBLACKBELT wrote:

eschn3am wrote:

Average is 4. Each of the pairs has an average of 4 except for B. which is 4 and D.

Answer B

??????? How can you deduce that (4+D)/2 isn't going to be 4?

I can't. It's a case of knowing that all the other ones are 4 for sure, so I'll put my money on the one that might be something else.

I agree that it's bizarre logic though. I'm thinking there must be something wrong with either the question, my logic or my understanding of the question because choosing B for being the lesser of 5 evils is ridiculous.

Re: PS: Standard Deviation [#permalink]
29 Jan 2008, 14:52

netcaesar wrote:

A set of data consists of the following 5 numbers: 0,2,4,6 and 8. Which 2 numbers, if added to create a set of 7 numbers, will result in a new standard deviation that is closest to the standard deviation for of the 5 original numbers?

A) -1 and 9 B) 4 and 4 C) 3 and 5 D) 2 and 6 E) 0 and 8

Sorry, I mistook and wrote d instead of 4 in B.

Average of 5 numbers = 4 The way I look at it is each of the choices will not affect the average (it remains 4 as the total will be 28 for 7 numbers), but the standard deviation will be least affected by choice B simply because (4-4)^2 will not affect the overall summation.