Practice Quiz 6
Statistics 0200
Fall 2007
Dr. Nancy Pfenning
1. (5 pts.) The proportion of all assaults on U.S. law enforcement officers that are made
with dangerous weapons (firearms, knives, etc. instead of hands, feet, fists, etc.) is
.20.
(a) What proportion should lie at the center of the distribution of sample proportions
of assaults made with dangerous weapons?
(b) The standard deviation of the distribution of sample proportion for samples of
size 64 is q.20(1 −.20)/64 = .05 as long as the sample is less than one tenth the
size of the population. Is it? (Answer yes or no.)
(c) The shape of the distribution of sample proportion is approximately normal as
long as the expected counts in and out of the category of interest are at least 10.
In samples of 64 assaults where overall .20 are made with dangerous weapons, we
expect to see about made with dangerous weapons and made with
hands, feet, fists, etc.
(d) Sketch a normal curve below showing the distribution of sample proportion of
assaults made with dangerous weapons for samples of size 64, using the center
from (a) and the standard deviation mentioned in (b), based on the 68-95-99.7
Rule.
(e) Suppose 8 in a sample of 64 assaults are made with dangerous weapons; this
proportion can be characterized as
(i) extremely low (ii) somewhat low (iii) somewhat high (iv) extremely high
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