NAME:
ANSWER KEY
Stat 205 Exam I
There are four problems total. Each lettered part of a problem is worth 7 points; there are 126
points total. However, your exam grade is out of 100 points, so there are 26 points of possible
extra credit. Write clearly and show steps for partial credit. This exam is open book.
1. The systolic blood pressure
Y
of a random American adult follows a normal distribution with
mean
μ
Y
= 127
mmHg and standard deviation
σ
Y
= 15
mmHg. Hypertension is deﬁned to
be
Y >
140
; hypotension (low blood pressure) is
Y <
90
.
(a) What is the probability of a randomly selected person having hypertension,
P
(
Y >
140)
?
Answer:
Using TI84, normalcdf(140,10
∧
99,127,15) gives 0.193. Using the table in
your book,
P
(
Y >
140) =
P
±
Y

127
15
>
140

127
15
¶
=
P
(
Z >
0
.
87)
= 1

P
(
Z <
0
.
87)
= 1

0
.
8078
≈
0
.
192
.
(b) What is the probability of a randomly selected person having low systolic blood pres
sure,
P
(
Y <
90)
?
Answer:
Using TI84, normalcdf(

10
∧
99,90,127,15) gives 0.007. Using the table in
your book,
P
(
Y <
90) =
P
±
Y

127
15
<
90

127
15
¶
=
P
(
Z <

2
.
45)
= 0
.
007
.
(c) What is the probability of a randomly selected person having normal systolic blood
pressure,
P
(90
< Y <
140)
?
Answer:
Using TI84, normalcdf(90,140,127,15) gives 0.800. Using the table in your
book,
P
(90
< Y <
140) =
P
±
90

127
15
<
Y

127
15
<
140

127
15
¶
=
P
(

2
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 Fall '09
 Hendrix
 systolic blood pressure, randomly selected person

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