Introduction to Geostatistics
Homework 3 – Due 25 February, 2008
Section 2.4 – Page 111
1.
Determine whether each of the following random variables is discrete or
continuous
a.
The number of heads in 100 tosses of a coin.
A
n
s
Discrete
 The number can only be an integer, so there are gaps
between the potential outcomes.
b.
The length of a rod randomly chosen from a day’s production.
Ans
Continuous
– If you (reasonably) assume that the measurement
contains many significant digits, then there are no gaps between outcomes.
c
The final exam score of a randomly chosen student from last
semester’s engineering statistics class.
Ans
Discrete
– Normally, it’s discrete because test grades will be
rounded to the nearest integer. Rarely would grades be given in
a continuous fashion.
d.
The age of a randomly chosen Colorado School of Mines student.
Ans
Continuous
– This really depends on how you record the age
(i.e. of you are rounding up/down). But like the example in class, the
outcomes are really continuous. For example, Mr. A is 25 yrs 10
months 15 days 21 hrs 12 mins 43.123345678 seconds.
e.
The age that randomly chosen Colorado School of Mines student will
be on his or her next birthday.
Ans
Discrete
– At the exact moment of the anniversary of one’s
birth, he/she is exactly n years old, so this RV only contains
integers.
2.
The following table presents the probability mass function of the number of
defects X in a randomly chosen printedcircuit board.
x0123
p
(
x
)
0
.
50
.
30
.
10
.
1
a Find P(X < 2)
Ans
P(X < 2)
=
P(X = 0) + P(X = 1)
=
0.5 + 0.3
=
0.8
b.
Find P(X >= 1)
Ans
P(X >= 1)
=
P(X = 1) + P(X = 2) + P(X =3)
=
0.3 + 0.1 + 0.1
=
0.5
c Find
x
μ
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentAns
=
x P(X = x)
=
0 * P(X=0) + 1 * P(X=1) + 2 * P(X=2)
+ 3*P(X = 3)
=
0 * 0.5 + 1 * 0.3 + 2 * 0.1 + 3 * 0.1
=
0.8
d
Find
Ans
=
( x 
)
2
P(x)
=
(00.8)
2
* 0.5 + (10.8)
2
* 0.3+
(20.8)
2
* 0.1 + (30.8)
2
* 0.1
=
0.96
3.
A chemical supply company ships a certain solvent in 10gallon drums. Let X
represent the number of drums ordered by a randomly chosen customer.
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 Jablonowski
 Probability theory, Probability mass function, y Ans Py

Click to edit the document details