2.1

7 a China

b 50 millions

c 350 millions

d the graph just shows the frequency of internet users in each country; the graph cannot tell the ratio of internet users within each country since each country has different population size.

9 a 69%

b 23/100 times 240 millions = 55.2 millions

c Inferential, because Gallup infers all American adults’views toward divorce from data taken from the sample.

11 a 18-34year old respondents: 0.43, 35-44 year old respondents:0.61

b 55+ year old respondents

c 18-34 year old respondents

d The older a respondent is, the more likelihood to buy when made in America.

13 a Total responses = 125+324+552+1257+2518= 4776

Relative Frequency

          never: 125/4776= 0.026
          
          Rarely: 324/4776=0.068
          
          Sometimes: 552/4776 =0.12
          
          Most of the times:1257/4776=0.26
          
          Always:2518/4776=0.53

b 0.53 times 100 =53%

C 0.026+0.068=0.094 times 100= 9.4%

d e f

my_data <- c(125, 324, 552, 1257,2518)

Responses <- c("Never", "Rarely", "Sometimes", "Most of the times", "Always")

barplot(my_data, main = "College students' behaviours of wearing a seat belt", names.arg = Responses)

barplot(my_data, main = "College students' behaviours of wearing a seat belt", names.arg = Responses, col = c("pink","light blue","light green","yellow"))

rel_freq <- my_data / sum(my_data)

barplot(rel_freq, main = "College students' behaviours of wearing a seat belt", names.arg = Responses, col = c("pink","light blue","light green","yellow"))

pie(my_data, labels = Responses, main = "College students' behaviours of wearing a seat belt")

g inferential

15 a total response: 377+192+132+81+243=1025

Relative frequency

More than 1 hour a day:377/1025=0.37

Up to 1 hour a day: 192/1025=0.19

A few times a week: 132/1025=0.13

Never:243/1025=0.24

b 0.24 times 100= 24%

c d e

my_data <- c(377, 192, 132, 81, 243)

Responses <- c("More than 1hour a day", "up to 1hour a day", "a few times a week", "a few times a month or less", "Never")

barplot(my_data, main = "personal usage of the Internet among 1025 adult Americans", names.arg = Responses)

barplot(my_data, main = "personal usage of the Internet among 1025 adult Americans", names.arg = Responses, col = c("pink","light blue","light green","yellow"))

rel_freq <- my_data / sum(my_data)

barplot(rel_freq, main = "personal usage of the Internet among 1025 adult Americans", names.arg = Responses, col = c("pink","light blue","light green","yellow"))

pie(my_data, labels = Responses, main = "personal usage of the Internet among 1025 adult Americans")

f 37% is the descriptive number from the samples of 1025 adult Americans. It cannot be simply generalized to the entire population unless it has the level of confidence.

2.2

9 a 8

b 2

c 15

d 4

e 15%

f skewed left distribution

10 a 12

b 2 weeks

c 2/(4+2+9+8+12+8+5+2+1+1)=0.03846 times 100=3.8%

d skewed right distribution

11 a 2+3+13+42+58+40+31+8+2+1=200 students

b 10

c 60-69:2, 70-79:3, 80-89;13, 90-99:42, 100-109:58, 110-119:40, 120-129:31, 130-139:8, 140-149:2, 150-159:1

d 100-109

e 150-159

f 11/200=0.055 times 100 =5.5%

g none

12 a 200

b 0-199, 200-399, 400-599, 600-799, 800-999, 1000-1199, 1200-1399, 1400-1599

c 0-199

d skewed right distribution

e population of Texas and Vermont are different. We cannot simply conclude which is safer than others by looking atnthe frequency number in the graph.

13 a bell shaped; Middle income class is the majority in the states and many other developed countries. The middle income class has the highest frequency while lower and higher income class have the less frequency.

b bell shaped; usually, only few people get score the highest and lowest score while majority of people get somewhat around average score.

c skewed right; frequent number of people would be 2~6 people and it is less common to have more than 6 people in a household at least in western countries. African countries may have the skewed left distribution since they tend to have a big family.

d skewed left; usually Alzheimer’s disease starts on later age of life. More older people would have the disease than younger people.

14 a skewed left; usually people drink on weekends.

b uniform; age of students should be same age.

c skewed left; often times, hearing aid patients are elderly.

d bell shaped; there are some people who are taller/shorter than average people but the majority people have somewhat around average height.

A histogram of sepal lengths

iris[1:10,]
##    Sepal.Length Sepal.Width Petal.Length Petal.Width Species
## 1           5.1         3.5          1.4         0.2  setosa
## 2           4.9         3.0          1.4         0.2  setosa
## 3           4.7         3.2          1.3         0.2  setosa
## 4           4.6         3.1          1.5         0.2  setosa
## 5           5.0         3.6          1.4         0.2  setosa
## 6           5.4         3.9          1.7         0.4  setosa
## 7           4.6         3.4          1.4         0.3  setosa
## 8           5.0         3.4          1.5         0.2  setosa
## 9           4.4         2.9          1.4         0.2  setosa
## 10          4.9         3.1          1.5         0.1  setosa
hist(iris$Sepal.Length)