Homework 6 Solutions
Yicheng Kang
October 29, 2010
6.30
z
=
x

μ
σ
=

.
75
which corresponds to a cumulative probability of 0
.
2266.
z
=
x

μ
σ
=
.
5
which corresponds to a cumulative probability of 0
.
6915. 0
.
6915

0
.
2266 = 0
.
4649(rounds to 0
.
46),
the approximate proportion of students who get a C.
6.61
z
= (258

281
.
9)
/
11
.
4 =

2
.
10; according to Table A, 0
.
0179 fall below this zscore; thus, propor
tion 0
.
018 of babies would be classiﬁed as premature.
7.20
a) The mean would be 8
.
20. Standard error =
σ/
√
n
= 3
/
√
100 = 0
.
30.
b)
z
= (8
,
95

8
.
20)
/
0
.
3 = 2
.
5.Table A tells us that 0
.
994 is the proportion below this zscore.
Thus, the probability that the restaurant makes a proﬁt that day is 0
.
994.
7.24
a)The center of the population distribution is the mean of the population of 60. The spread is the
standard deviation of the population,16.
1
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View Full Documentb)The center of the data distribution 58
.
3 The spread is the standard deviation of 15
.
0. It is
probably skewed to the left.
c) The center of the sampling distribution mean is 60. The spread, or standard error, is
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 Spring '11
 Normal Distribution, Probability, Standard Deviation, Standard Error, Yicheng Kang

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