ENGINEERS
SPRING 2010
SAMPLE MIDTERM 1 EXAM
Problem 1
A university librarian produced the following probability distribution of the number
of times a student walks into the library over the period of a semester.
x
0
5
10
15
20
25
30
40
50
75
100
p
(
x
) .22 .29 .12 .09 .08 .05 .04 .04 .03 .03
.01
(a)
Calculate the mean of
X
.
(b)
Calculate the standard deviation of
X
.
Problem 2
The following data represent the birth weights (in grams) of babies born in 2002
along with the period of gestation.
Birth Weight
Period of Gestation
(in grams)
Preterm
Term
Postterm
Total
Less than 1000
28,247
202
32
28,481
1000-1999
78,532
10,325
1,051
89,908
2000-2999
228,064
606,046
39,481
873,591
3000-3999
135,790
2,293,927
192,566
2,622,283
4000-5000
8,974
315,821
34,319
359,114
Over 5000
211
4,524
556
5,291
Total
479,818
3,230,845
268,005
3,978,668
(a)
What is the probability that a randomly selected baby born in 2002 was
preterm?
(b)
What is the probability that a randomly selected baby born in 2002 weighted
less than 3000 grams?
1