STAT 113 Week 15 (Apr 15)
Work Sheet 10: Chapter 24
**Write down the type of probability (joint, marginal or conditional) for each
question on this worksheet**
1. Here are counts from a study of all firearm-related deaths in Wisconsin between
2000 and 2002 for children and youth under the age of 25 where the type of
firearm used was known. We want to compare the types of firearms used in
homicides and in suicides.
Handgun
Long gun
Homicides
106
17
Suicides
59
166
(a) What percent of deaths were suicides and used handguns?
59/(106+59+17+166)=16.95%, joint
(b) What percent of homicides used long guns?
17/(106+17)=13.82%, conditional
(c) Long guns were used in what percent of deaths?
(17+166)/ (106+59+17+166)=52.59%, marginal
2. Here is a table that breaks down Purdue’s 1697 faculty members by both gender
and academic rank:
Female
Male
Assistant professors
151
254
Associate professors
154
397
Professors
99
642
(a) What percent of the faculty members are female?
(151+154+99)/1697=23.81%, marginal
(b) Among male faculty members, what is the percent who are professors?
642/(254+397+642) =49.65%, conditional
(c) What percent of the faculty members are female associate professors?
154/1697=9.07%, joint
(d) What percent of female faculty members were associate professors or professors?
(154+99)/(151+154+99)=62.62%, conditional
3. How is the hatching of water python eggs influenced by the temperature of the
snake’s nest? Researchers assigned newly laid eggs to one of three temperature:
hot, neutral, or cold. Hot duplicated the extra warmth provided by the mother
python, and cold duplicated the absence of the mother. Here are the data on the
number of eggs and the number that hatched:
Number of eggs
Hatched
Cold
27
16
Neutral
56
38
Hot
104
75
(a) Make a two-way table of temperature by outcome (hatched or not)
Not hatched
Hatched
Cold
11
16
Neutral
18
38
Hot
29
75
(b) What percent of newly laid eggs were assigned to cold?
27/187=14.44%, marginal
(c) What percent of newly laid eggs were assigned to neutral and hatched?
38/187=20.32%, joint
(d) Find the conditional distribution of temperature for hatched eggs and draw a
labeled bar graph to display this distribution.
16/129=12.40%, 38/129=29.46%, 75/129=58.14%,
percent
80
58.14%
60
40
20
29.46%
12.40%
0
cold
neutral
hot
temperature for hatched eggs
4. Below are the numbers of flights on time and delayed for Alaska Airlines at five
airports in one month.
On time
Delayed
Los Angeles
497
62
Phoenix
221
12
San Diego
212
20
San Francisco
503
102
Seattle
1841
305
(a)
Among the flights to Los Angeles, what percent of flights were delayed?
62/(497+62)=11.09%, conditional
(b) What percent of delayed flights were not flying to Los Angeles?
100%-62/(62+12+20+102+305)=87.62%, conditional
Or (12+20+102+305)/(62+12+20+102+305)=87.62%
(c) What percent of flights were on time?
(497+221+212+503+1841)/(497+221+212+503+1841+62+12+
20+102+305)
=86.72%, Marginal
(d) What percent of flights were on time and the destination is Phoenix or San Diego?
(221+212)/total = 11.47%, joint