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(SD) of the four

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(SD) of the four

by sanju09 » Tue Nov 10, 2009 2:05 am
What is the standard deviation (SD) of the four numbers p, q, r, and 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: — Data Sufficiency |
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by italian7745 » Tue Nov 10, 2009 3:33 am
IMO C[/b]
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by italian7745 » Tue Nov 10, 2009 3:48 am
Repeat Post
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by xcusemeplz2009 » Tue Nov 10, 2009 3:51 am
IMO C
sd=square rut of summation(xi-xm)^2
xi is the items
xm is the mean
summation of (xi-xm)^2=(x1-xm)^2+(x2-xm)^2+....so on
s 1)
x1+x2+x3+x4=24
xm=6 (24/4)
not suff we dnt have values for x1,x2,x3 and x4

s2)
x1^2+x2^2+x3^2+x4^2=224

not suff..reason same for s1

combining
yes
sd=sqrt[(x1-6)^2+(x2-6)^2+(x3-6)^2+(x4-6)^2]
on simplifying
sd=[x1^2+x2^2+x3^2+x4^2]-12(x1+x2+x3+x4)+4*36
hence C
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