Statistics 324 (Bates)
Midterm 1
20081009 (p. 1)
Choose the most appropriate answer. Mark only one selection. Use pencil.
1. In a single sample of data the 50th percentile is also called the sample (a) mean (b) median
(c) range (d) standard deviation (e) variance
2. The formula for the sample standard deviation,
s
, is (a)
p
(
∑
n
i
=1
x
i
)
/n
(b)
p
(
∑
n
i
=1
(
x
i

¯
x
)
2
)
/n
(c)
p
(
∑
n
i
=1
(
x
i

¯
x
)
2
)
/
(
n

1) (d)
(∑
n
i
=1
(
x
i

¯
x
)
2
)
/n
(e)
(∑
n
i
=1
(
x
i

¯
x
)
2
)
/
(
n

1).
3. If
s
is the sample standard deviation and ¯
x
is the sample mean we expect about 95% of the
data to fall in the interval (a)
s
±
¯
x
(b)
s
±
2¯
x
(c) ¯
x
±
s
(d) ¯
x
±
2
s
(e) ¯
x
±
3
s
4. The box in a boxandwhisker plot covers what portion of the data? (a) 50% (b) 2/3 (c) 95%
(d) 99% (e) no speciﬁc proportion  it will vary.
5. For a continuous random variable
X
, which statement is
not
always true of the probability
density function,
f
(
x
)? (a) 0
≤
f
(
x
) (b)
f
(
x
)
≤
1 (c)
R
∞
∞
f
(
x
)
dx
= 1 (d)
P
[
a
≤
X
≤
b
] =
R
b
a
f
(
x
)
dx
(e)
P
[
a
≤
X < b
] =
R
b
a
f
(
x
)
dx
6. Which distribution is most commonly used to model the time to failure of a system? (a) bi
nomial (b) Poisson (c) normal (or Gaussian) (d) uniform (e) exponential
7. Which distribution is a continuous distribution? (a) binomial (b) geometric (c) hypergeomet
ric (d) negative binomial (e) normal (or Gaussian)
8. A binomial random variable,
X
, models the total number of successes in
n
independent,
identical trials, each with probability
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 Fall '08
 Bates
 Statistics, Normal Distribution, Standard Deviation, Bates

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