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Given a population with
μ
= 10 and
σ
=
20,
1. What value is exactly 75 percent of the data lower then?
2. What is the percentile of the value 0?
3. What value is below exactly 60 percent of the data?
4. What proportion of the data falls outside values of 30 and 15?
5. What percent of the data are higher than 14?
6. What value is above exactly 10 percent of the data?
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μ
= 10 and
σ
=
20,
1. What value is exactly 75 percent of the data lower then?
.75
x:
10
?
z:
0
?
Calculate the just the area above the mean: .75  .5 = .25
For an area of .25 in column B, lookup corresponding z score in column A: ~.67
Convert zscore to data value, x = (z)(
σ
) + μ = (.67)(20) 10 = 3.4
2. What is the percentile of the value 0?
Convert to zvalue: z =
(xμ)/
σ
= (0+10)/20 = .5
?
x:
10
XX
z:
0
ZZ
Either: For z = .5 in column A, lookup the corresponding area from column C: .3085
1  .3085 = .6915
(.6915)100=.6915
The 69th percentile.
Or:
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 Fall '08
 Ard

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