DS...SD...

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ontopofit: Senior | Next Rank: 100 Posts; Posts: 68; Joined: Sun Dec 21, 2008 12:00 am; Thanked: 3 times

by ontopofit » Thu Feb 19, 2009 12:47 pm

What is the standard deviation (SD) of the four numbers p, q, r, s?
1. The sum of p, q, r and s is 24
2. The sum of the squares of p, q, r and s is 224

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Source: Beat The GMAT — Data Sufficiency | Thu Feb 19, 2009 12:47 pm

x2suresh: Master | Next Rank: 500 Posts; Posts: 258; Joined: Thu Aug 07, 2008 5:32 am; Thanked: 16 times

Re: DS...SD...

by x2suresh » Thu Feb 19, 2009 2:33 pm

ontopofit wrote:What is the standard deviation (SD) of the four numbers p, q, r, s?
1. The sum of p, q, r and s is 24
2. The sum of the squares of p, q, r and s is 224

C .

VARIANCE =SD^2 = 1/N { SUM (Squares of numbers) - Avg(numbers)^2 }
= 1/4*(224 - 36)

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